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/Scala 2.13 Library

Class scala.collection.immutable.List

Companion object List

sealed abstract class List[+A] extends AbstractSeq[A] with LinearSeq[A] with LinearSeqOps[A, List, List[A]] with StrictOptimizedLinearSeqOps[A, List, List[A]] with StrictOptimizedSeqOps[A, List, List[A]] with IterableFactoryDefaults[A, List] with DefaultSerializable

A class for immutable linked lists representing ordered collections of elements of type A.

This class comes with two implementing case classes scala.Nil and scala.:: that implement the abstract members isEmpty, head and tail.

This class is optimal for last-in-first-out (LIFO), stack-like access patterns. If you need another access pattern, for example, random access or FIFO, consider using a collection more suited to this than List.

Performance

Time: List has O(1) prepend and head/tail access. Most other operations are O(n) on the number of elements in the list. This includes the index-based lookup of elements, length, append and reverse.

Space: List implements structural sharing of the tail list. This means that many operations are either zero- or constant-memory cost.

val mainList = List(3, 2, 1)
val with4 =    4 :: mainList  // re-uses mainList, costs one :: instance
val with42 =   42 :: mainList // also re-uses mainList, cost one :: instance
val shorter =  mainList.tail  // costs nothing as it uses the same 2::1::Nil instances as mainList
Annotations
@SerialVersionUID()
Source
List.scala
Example:
  1. // Make a list via the companion object factory
    val days = List("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")
    
    // Make a list element-by-element
    val when = "AM" :: "PM" :: Nil
    
    // Pattern match
    days match {
      case firstDay :: otherDays =>
        println("The first day of the week is: " + firstDay)
      case Nil =>
        println("There don't seem to be any week days.")
    }
Since

1.0

Note

The functional list is characterized by persistence and structural sharing, thus offering considerable performance and space consumption benefits in some scenarios if used correctly. However, note that objects having multiple references into the same functional list (that is, objects that rely on structural sharing), will be serialized and deserialized with multiple lists, one for each reference to it. I.e. structural sharing is lost after serialization/deserialization.

See also

"Scala's Collection Library overview" section on Lists for more information.

Linear Supertypes
DefaultSerializable, java.io.Serializable, StrictOptimizedSeqOps[A, List, List[A]], StrictOptimizedLinearSeqOps[A, List, List[A]], collection.StrictOptimizedSeqOps[A, List, List[A]], StrictOptimizedIterableOps[A, List, List[A]], LinearSeq[A], LinearSeqOps[A, [X]List[X], List[A]], collection.LinearSeq[A], collection.LinearSeqOps[A, [X]List[X], List[A]], AbstractSeq[A], Seq[A], SeqOps[A, [_]List[_], List[A]], Iterable[A], collection.AbstractSeq[A], collection.Seq[A], Equals, collection.SeqOps[A, [_]List[_], List[A]], PartialFunction[Int, A], (Int) => A, AbstractIterable[A], collection.Iterable[A], IterableFactoryDefaults[A, [x]List[x]], IterableOps[A, [_]List[_], List[A]], IterableOnceOps[A, [_]List[_], List[A]], IterableOnce[A], AnyRef, Any
Known Subclasses
::, Nil

Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

true if !(this == that), false otherwise.

Definition Classes
AnyRef → Any

final def ##(): Int

Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any

def +(other: String): String

Implicit
This member is added by an implicit conversion from List[A] toany2stringadd[List[A]] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

final def ++[B >: A](suffix: IterableOnce[B]): List[B]

Alias for concat

Definition Classes
IterableOps
Annotations
@inline()

final def ++:[B >: A](prefix: IterableOnce[B]): List[B]

Alias for prependedAll

Definition Classes
SeqOpsIterableOps
Annotations
@inline()

final def +:[B >: A](elem: B): List[B]

Alias for prepended.

Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.

Definition Classes
SeqOps
Annotations
@inline()

def ->[B](y: B): (List[A], B)

Implicit
This member is added by an implicit conversion from List[A] toArrowAssoc[List[A]] performed by method ArrowAssoc in scala.Predef.This conversion will take place only if A is a subclass of Option[Nothing] (A <: Option[Nothing]).
Definition Classes
ArrowAssoc
Annotations
@inline()

final def :+[B >: A](elem: B): List[B]

Alias for appended

Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.

Definition Classes
SeqOps
Annotations
@inline()

final def :++[B >: A](suffix: IterableOnce[B]): List[B]

Alias for appendedAll

Definition Classes
SeqOps
Annotations
@inline()

def ::[B >: A](elem: B): List[B]

Adds an element at the beginning of this list.

elem

the element to prepend.

returns

a list which contains x as first element and which continues with this list. Example:

1 :: List(2, 3) = List(2, 3).::(1) = List(1, 2, 3)

def :::[B >: A](prefix: List[B]): List[B]

Adds the elements of a given list in front of this list.

Example:

List(1, 2) ::: List(3, 4) = List(3, 4).:::(List(1, 2)) = List(1, 2, 3, 4)
prefix

The list elements to prepend.

returns

a list resulting from the concatenation of the given list prefix and this list.

final def ==(arg0: Any): Boolean

The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

final def addString(b: mutable.StringBuilder): mutable.StringBuilder

Appends all elements of this collection to a string builder. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection without any separator string.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> val h = a.addString(b)
h: StringBuilder = 1234
b

the string builder to which elements are appended.

returns

the string builder b to which elements were appended.

Definition Classes
IterableOnceOps
Annotations
@inline()

final def addString(b: mutable.StringBuilder, sep: String): mutable.StringBuilder

Appends all elements of this collection to a string builder using a separator string. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection, separated by the string sep.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> a.addString(b, ", ")
res0: StringBuilder = 1, 2, 3, 4
b

the string builder to which elements are appended.

sep

the separator string.

returns

the string builder b to which elements were appended.

Definition Classes
IterableOnceOps
Annotations
@inline()

def addString(b: mutable.StringBuilder, start: String, sep: String, end: String): mutable.StringBuilder

Appends all elements of this collection to a string builder using start, end, and separator strings. The written text begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

scala> a.addString(b , "List(" , ", " , ")")
res5: StringBuilder = List(1, 2, 3, 4)
b

the string builder to which elements are appended.

start

the starting string.

sep

the separator string.

end

the ending string.

returns

the string builder b to which elements were appended.

Definition Classes
IterableOnceOps

def andThen[C](k: PartialFunction[A, C]): PartialFunction[Int, C]

Composes this partial function with another partial function that gets applied to results of this partial function.

Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. It is highly recommended to call applyOrElse instead of isDefinedAt / apply for efficiency.

C

the result type of the transformation function.

k

the transformation function

returns

a partial function with the domain of this partial function narrowed by other partial function, which maps arguments x to k(this(x)).

Definition Classes
PartialFunction

def andThen[C](k: (A) => C): PartialFunction[Int, C]

Composes this partial function with a transformation function that gets applied to results of this partial function.

If the runtime type of the function is a PartialFunction then the other andThen method is used (note its cautions).

C

the result type of the transformation function.

k

the transformation function

returns

a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments x to k(this(x)).

Definition Classes
PartialFunctionFunction1

def appended[B >: A](elem: B): List[B]

A copy of this sequence with an element appended.

Note: will not terminate for infinite-sized collections.

Example:

scala> val a = List(1)
a: List[Int] = List(1)

scala> val b = a :+ 2
b: List[Int] = List(1, 2)

scala> println(a)
List(1)
B

the element type of the returned sequence.

elem

the appended element

returns

a new sequence consisting of all elements of this sequence followed by value.

Definition Classes
StrictOptimizedSeqOpsSeqOps

def appendedAll[B >: A](suffix: IterableOnce[B]): List[B]

Returns a new list containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the list is the most specific superclass encompassing the element types of the two operands.

B

the element type of the returned collection.

suffix

the iterable to append.

returns

a new collection of type CC[B] which contains all elements of this list followed by all elements of suffix.

Definition Classes
ListStrictOptimizedSeqOpsSeqOps

def apply(n: Int): A

Get the element at the specified index. This operation is provided for convenience in Seq. It should not be assumed to be efficient unless you have an IndexedSeq.

Definition Classes
LinearSeqOpsSeqOps
Annotations
@throws(scala.this.throws.<init>$default$1[IndexOutOfBoundsException])

def applyOrElse[A1 <: Int, B1 >: A](x: A1, default: (A1) => B1): B1

Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.

Note that expression pf.applyOrElse(x, default) is equivalent to

if(pf isDefinedAt x) pf(x) else default(x)

except that applyOrElse method can be implemented more efficiently. For all partial function literals the compiler generates an applyOrElse implementation which avoids double evaluation of pattern matchers and guards. This makes applyOrElse the basis for the efficient implementation for many operations and scenarios, such as:

    combining partial functions into orElse/andThen chains does not lead to excessive apply/isDefinedAt evaluation lift and unlift do not evaluate source functions twice on each invocation runWith allows efficient imperative-style combining of partial functions with conditionally applied actions

For non-literal partial function classes with nontrivial isDefinedAt method it is recommended to override applyOrElse with custom implementation that avoids double isDefinedAt evaluation. This may result in better performance and more predictable behavior w.r.t. side effects.

x

the function argument

default

the fallback function

returns

the result of this function or fallback function application.

Definition Classes
PartialFunction
Since

2.10

final def asInstanceOf[T0]: T0

Cast the receiver object to be of type T0.

Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

returns

the receiver object.

Definition Classes
Any
Exceptions thrown

ClassCastException if the receiver object is not an instance of the erasure of type T0.

def canEqual(that: Any): Boolean

Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.

that

The object with which this sequence should be compared

returns

true, if this sequence can possibly equal that, false otherwise. The test takes into consideration only the run-time types of objects but ignores their elements.

Definition Classes
SeqEquals

def className: String

Defines the prefix of this object's toString representation.

It is recommended to return the name of the concrete collection type, but not implementation subclasses. For example, for ListMap this method should return "ListMap", not "Map" (the supertype) or "Node" (an implementation subclass).

The default implementation returns "Iterable". It is overridden for the basic collection kinds "Seq", "IndexedSeq", "LinearSeq", "Buffer", "Set", "Map", "SortedSet", "SortedMap" and "View".

returns

a string representation which starts the result of toString applied to this list. By default the string prefix is the simple name of the collection class list.

Attributes
protected[this]
Definition Classes
ListIterable

def clone(): AnyRef

Create a copy of the receiver object.

The default implementation of the clone method is platform dependent.

returns

a copy of the receiver object.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note

not specified by SLS as a member of AnyRef

final def coll: List.this.type

returns

This collection as a C.

Attributes
protected
Definition Classes
IterableIterableOps

final def collect[B](pf: PartialFunction[A, B]): List[B]

Builds a new list by applying a partial function to all elements of this list on which the function is defined.

B

the element type of the returned list.

pf

the partial function which filters and maps the list.

returns

a new list resulting from applying the given partial function pf to each element on which it is defined and collecting the results. The order of the elements is preserved.

Definition Classes
ListStrictOptimizedIterableOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def collectFirst[B](pf: PartialFunction[A, B]): Option[B]

Finds the first element of the collection for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

pf

the partial function

returns

an option value containing pf applied to the first value for which it is defined, or None if none exists.

Definition Classes
IterableOnceOps
Example:

    Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)

def combinations(n: Int): Iterator[List[A]]

Iterates over combinations. A _combination_ of length n is a subsequence of the original sequence, with the elements taken in order. Thus, "xy" and "yy" are both length-2 combinations of "xyy", but "yx" is not. If there is more than one way to generate the same subsequence, only one will be returned.

For example, "xyyy" has three different ways to generate "xy" depending on whether the first, second, or third "y" is selected. However, since all are identical, only one will be chosen. Which of the three will be taken is an implementation detail that is not defined.

Note: Even when applied to a view or a lazy collection it will always force the elements.

returns

An Iterator which traverses the possible n-element combinations of this sequence.

Definition Classes
SeqOps
Example:

    "abbbc".combinations(2) = Iterator(ab, ac, bb, bc)

def compose[R](k: PartialFunction[R, Int]): PartialFunction[R, A]

Composes another partial function k with this partial function so that this partial function gets applied to results of k.

Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. It is highly recommended to call applyOrElse instead of isDefinedAt / apply for efficiency.

R

the parameter type of the transformation function.

k

the transformation function

returns

a partial function with the domain of other partial function narrowed by this partial function, which maps arguments x to this(k(x)).

Definition Classes
PartialFunction

def compose[A](g: (A) => Int): (A) => A

Composes two instances of Function1 in a new Function1, with this function applied last.

A

the type to which function g can be applied

g

a function A => T1

returns

a new function f such that f(x) == apply(g(x))

Definition Classes
Function1
Annotations
@unspecialized()

final def concat[B >: A](suffix: IterableOnce[B]): List[B]

Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the sequence is the most specific superclass encompassing the element types of the two operands.

B

the element type of the returned collection.

suffix

the traversable to append.

returns

a new sequence which contains all elements of this sequence followed by all elements of suffix.

Definition Classes
SeqOpsIterableOps
Annotations
@inline()

final def contains[A1 >: A](elem: A1): Boolean

Tests whether this list contains a given value as an element.

elem

the element to test.

returns

true if this list has an element that is equal (as determined by ==) to elem, false otherwise.

Definition Classes
ListLinearSeqOpsSeqOps

def containsSlice[B](that: collection.Seq[B]): Boolean

Tests whether this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

that

the sequence to test

returns

true if this sequence contains a slice with the same elements as that, otherwise false.

Definition Classes
SeqOps

def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Int

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with at most len elements of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached, or len elements have been copied.

B

the type of the elements of the array.

xs

the array to fill.

start

the starting index of xs.

len

the maximal number of elements to copy.

returns

the number of elements written to the array

Definition Classes
IterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change. Note: will not terminate for infinite-sized collections.

def copyToArray[B >: A](xs: Array[B], start: Int): Int

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.

B

the type of the elements of the array.

xs

the array to fill.

start

the starting index of xs.

returns

the number of elements written to the array Note: will not terminate for infinite-sized collections.

Definition Classes
IterableOnceOps

def copyToArray[B >: A](xs: Array[B]): Int

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.

B

the type of the elements of the array.

xs

the array to fill.

returns

the number of elements written to the array Note: will not terminate for infinite-sized collections.

Definition Classes
IterableOnceOps

def corresponds[B](that: collection.Seq[B])(p: (A, B) => Boolean): Boolean

Tests whether every element of this list relates to the corresponding element of another sequence by satisfying a test predicate.

B

the type of the elements of that

that

the other sequence

p

the test predicate, which relates elements from both sequences

returns

true if both sequences have the same length and p(x, y) is true for all corresponding elements x of this list and y of that, otherwise false.

Definition Classes
ListSeqOps

def corresponds[B](that: IterableOnce[B])(p: (A, B) => Boolean): Boolean

Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.

B

the type of the elements of that

that

the other collection

p

the test predicate, which relates elements from both collections

returns

true if both collections have the same length and p(x, y) is true for all corresponding elements x of this iterator and y of that, otherwise false

Definition Classes
IterableOnceOps

def count(p: (A) => Boolean): Int

Counts the number of elements in the collection which satisfy a predicate.

p

the predicate used to test elements.

returns

the number of elements satisfying the predicate p.

Definition Classes
IterableOnceOps

def diff[B >: A](that: collection.Seq[B]): List[A]

Computes the multiset difference between this sequence and another sequence.

that

the sequence of elements to remove

returns

a new sequence which contains all elements of this sequence except some of occurrences of elements that also appear in that. If an element value x appears n times in that, then the first n occurrences of x will not form part of the result, but any following occurrences will.

Definition Classes
StrictOptimizedSeqOpsSeqOps

def distinct: List[A]

Selects all the elements of this sequence ignoring the duplicates.

returns

a new sequence consisting of all the elements of this sequence without duplicates.

Definition Classes
SeqOps

def distinctBy[B](f: (A) => B): List[A]

Selects all the elements of this immutable sequence ignoring the duplicates as determined by == after applying the transforming function f.

B

the type of the elements after being transformed by f

f

The transforming function whose result is used to determine the uniqueness of each element

returns

a new immutable sequence consisting of all the elements of this immutable sequence without duplicates.

Definition Classes
StrictOptimizedSeqOpsStrictOptimizedSeqOpsSeqOps

def drop(n: Int): List[A]

Selects all elements except first n ones.

n

the number of elements to drop from this sequence.

returns

a sequence consisting of all elements of this sequence except the first n ones, or else the empty sequence, if this sequence has less than n elements. If n is negative, don't drop any elements.

Definition Classes
StrictOptimizedLinearSeqOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def dropRight(n: Int): List[A]

The rest of the collection without its n last elements. For linear, immutable collections this should avoid making a copy.

Note: Even when applied to a view or a lazy collection it will always force the elements.

n

the number of elements to drop from this iterable collection.

returns

a iterable collection consisting of all elements of this iterable collection except the last n ones, or else the empty iterable collection, if this iterable collection has less than n elements. If n is negative, don't drop any elements.

Definition Classes
StrictOptimizedIterableOpsIterableOps

def dropWhile(p: (A) => Boolean): List[A]

Drops longest prefix of elements that satisfy a predicate.

p

The predicate used to test elements.

returns

the longest suffix of this sequence whose first element does not satisfy the predicate p.

Definition Classes
StrictOptimizedLinearSeqOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def elementWise: ElementWiseExtractor[Int, A]

Returns an extractor object with a unapplySeq method, which extracts each element of a sequence data.

Definition Classes
PartialFunction
Example:
    val firstChar: String => Option[Char] = _.headOption
    
    Seq("foo", "bar", "baz") match {
      case firstChar.unlift.elementWise(c0, c1, c2) =>
        println(s"$c0, $c1, $c2") // Output: f, b, b
    }

def empty: List[A]

The empty iterable of the same type as this iterable

returns

an empty iterable of type C.

Definition Classes
IterableFactoryDefaultsIterableOps

def endsWith[B >: A](that: collection.Iterable[B]): Boolean

Tests whether this sequence ends with the given sequence.

Note: will not terminate for infinite-sized collections.

that

the sequence to test

returns

true if this sequence has that as a suffix, false otherwise.

Definition Classes
SeqOps

def ensuring(cond: (List[A]) => Boolean, msg: => Any): List[A]

Implicit
This member is added by an implicit conversion from List[A] toEnsuring[List[A]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: (List[A]) => Boolean): List[A]

Implicit
This member is added by an implicit conversion from List[A] toEnsuring[List[A]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean, msg: => Any): List[A]

Implicit
This member is added by an implicit conversion from List[A] toEnsuring[List[A]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean): List[A]

Implicit
This member is added by an implicit conversion from List[A] toEnsuring[List[A]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

final def eq(arg0: AnyRef): Boolean

Tests whether the argument (that) is a reference to the receiver object (this).

The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false. null.eq(null) returns true.

When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

returns

true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def equals(o: Any): Boolean

The universal equality method defined in AnyRef.

Definition Classes
ListSeqEquals → AnyRef → Any

final def exists(p: (A) => Boolean): Boolean

Tests whether a predicate holds for at least one element of this list.

p

the predicate used to test elements.

returns

true if the given predicate p is satisfied by at least one element of this list, otherwise false

Definition Classes
ListLinearSeqOpsIterableOnceOps

def filter(p: (A) => Boolean): List[A]

Selects all elements of this list which satisfy a predicate.

p

the predicate used to test elements.

returns

a new iterator consisting of all elements of this list that satisfy the given predicate p. The order of the elements is preserved.

Definition Classes
ListStrictOptimizedIterableOpsIterableOpsIterableOnceOps

def filterImpl(pred: (A) => Boolean, isFlipped: Boolean): List[A]

Attributes
protected[scala.collection]
Definition Classes
StrictOptimizedIterableOps

def filterNot(p: (A) => Boolean): List[A]

Selects all elements of this list which do not satisfy a predicate.

returns

a new list consisting of all elements of this list that do not satisfy the given predicate pred. Their order may not be preserved.

Definition Classes
ListStrictOptimizedIterableOpsIterableOpsIterableOnceOps

def finalize(): Unit

Called by the garbage collector on the receiver object when there are no more references to the object.

The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note

not specified by SLS as a member of AnyRef

final def find(p: (A) => Boolean): Option[A]

Finds the first element of the list satisfying a predicate, if any.

p

the predicate used to test elements.

returns

an option value containing the first element in the list that satisfies p, or None if none exists.

Definition Classes
ListLinearSeqOpsIterableOnceOps

def findLast(p: (A) => Boolean): Option[A]

Finds the last element of the sequence satisfying a predicate, if any.

Note: will not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

an option value containing the last element in the sequence that satisfies p, or None if none exists.

Definition Classes
LinearSeqOpsSeqOps

final def flatMap[B](f: (A) => IterableOnce[B]): List[B]

Builds a new list by applying a function to all elements of this list and using the elements of the resulting collections.

For example:

def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")

The type of the resulting collection is guided by the static type of list. This might cause unexpected results sometimes. For example:

// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)

// lettersOf will return a Set[Char], not a Seq
def lettersOf(words: Seq[String]) = words.toSet flatMap ((word: String) => word.toSeq)

// xs will be an Iterable[Int]
val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)

// ys will be a Map[Int, Int]
val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)
B

the element type of the returned collection.

f

the function to apply to each element.

returns

a new list resulting from applying the given collection-valued function f to each element of this list and concatenating the results.

Definition Classes
ListStrictOptimizedIterableOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def flatten[B](implicit toIterableOnce: (A) => IterableOnce[B]): List[B]

Converts this iterable collection of traversable collections into a iterable collection formed by the elements of these traversable collections.

The resulting collection's type will be guided by the type of iterable collection. For example:

val xs = List(
           Set(1, 2, 3),
           Set(1, 2, 3)
         ).flatten
// xs == List(1, 2, 3, 1, 2, 3)

val ys = Set(
           List(1, 2, 3),
           List(3, 2, 1)
         ).flatten
// ys == Set(1, 2, 3)
B

the type of the elements of each traversable collection.

returns

a new iterable collection resulting from concatenating all element iterable collections.

Definition Classes
StrictOptimizedIterableOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def fold[A1 >: A](z: A1)(op: (A1, A1) => A1): A1

Folds the elements of this collection using the specified associative binary operator. The default implementation in IterableOnce is equivalent to foldLeft but may be overridden for more efficient traversal orders.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

Note: will not terminate for infinite-sized collections.

A1

a type parameter for the binary operator, a supertype of A.

z

a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g., Nil for list concatenation, 0 for addition, or 1 for multiplication).

op

a binary operator that must be associative.

returns

the result of applying the fold operator op between all the elements and z, or z if this collection is empty.

Definition Classes
IterableOnceOps

def foldLeft[B](z: B)(op: (B, A) => B): B

Applies a binary operator to a start value and all elements of this sequence, going left to right.

Note: will not terminate for infinite-sized collections.

B

the result type of the binary operator.

z

the start value.

op

the binary operator.

returns

the result of inserting op between consecutive elements of this sequence, going left to right with the start value z on the left:

op(...op(z, x_1), x_2, ..., x_n)

where x1, ..., xn are the elements of this sequence. Returns z if this sequence is empty.

Definition Classes
LinearSeqOpsIterableOnceOps

final def foldRight[B](z: B)(op: (A, B) => B): B

Applies a binary operator to all elements of this list and a start value, going right to left.

B

the result type of the binary operator.

z

the start value.

op

the binary operator.

returns

the result of inserting op between consecutive elements of this list, going right to left with the start value z on the right:

op(x_1, op(x_2, ... op(x_n, z)...))

where x1, ..., xn are the elements of this list. Returns z if this list is empty.

Definition Classes
ListIterableOnceOps

final def forall(p: (A) => Boolean): Boolean

Tests whether a predicate holds for all elements of this list.

p

the predicate used to test elements.

returns

true if this list is empty or the given predicate p holds for all elements of this list, otherwise false.

Definition Classes
ListLinearSeqOpsIterableOnceOps

final def foreach[U](f: (A) => U): Unit

Apply f to each element for its side effects Note: [U] parameter needed to help scalac's type inference.

Definition Classes
ListLinearSeqOpsIterableOnceOps
Annotations
@inline()

def formatted(fmtstr: String): String

Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Implicit
This member is added by an implicit conversion from List[A] toStringFormat[List[A]] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()

def fromSpecific(coll: IterableOnce[A]): List[A]

Defines how to turn a given Iterable[A] into a collection of type C.

This process can be done in a strict way or a non-strict way (ie. without evaluating the elements of the resulting collections). In other words, this methods defines the evaluation model of the collection.

Attributes
protected
Definition Classes
IterableFactoryDefaultsIterableOps
Note

When implementing a custom collection type and refining C to the new type, this method needs to be overridden (the compiler will issue an error otherwise). In the common case where C =:= CC[A], this can be done by mixing in the IterableFactoryDefaults trait, which implements the method using iterableFactory.

,

As witnessed by the @uncheckedVariance annotation, using this method might be unsound. However, as long as it is called with an Iterable[A] obtained from this collection (as it is the case in the implementations of operations where we use a View[A]), it is safe.

final def getClass(): Class[_ <: AnyRef]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

def groupBy[K](f: (A) => K): Map[K, List[A]]

Partitions this iterable collection into a map of iterable collections according to some discriminator function.

Note: Even when applied to a view or a lazy collection it will always force the elements.

K

the type of keys returned by the discriminator function.

f

the discriminator function.

returns

A map from keys to iterable collections such that the following invariant holds:

(xs groupBy f)(k) = xs filter (x => f(x) == k)

That is, every key k is bound to a iterable collection of those elements x for which f(x) equals k.

Definition Classes
IterableOps

def groupMap[K, B](key: (A) => K)(f: (A) => B): Map[K, List[B]]

Partitions this iterable collection into a map of iterable collections according to a discriminator function key. Each element in a group is transformed into a value of type B using the value function.

It is equivalent to groupBy(key).mapValues(_.map(f)), but more efficient.

case class User(name: String, age: Int)

def namesByAge(users: Seq[User]): Map[Int, Seq[String]] =
  users.groupMap(_.age)(_.name)

Note: Even when applied to a view or a lazy collection it will always force the elements.

K

the type of keys returned by the discriminator function

B

the type of values returned by the transformation function

key

the discriminator function

f

the element transformation function

Definition Classes
IterableOps

def groupMapReduce[K, B](key: (A) => K)(f: (A) => B)(reduce: (B, B) => B): Map[K, B]

Partitions this iterable collection into a map according to a discriminator function key. All the values that have the same discriminator are then transformed by the value function and then reduced into a single value with the reduce function.

It is equivalent to groupBy(key).mapValues(_.map(f).reduce(reduce)), but more efficient.

def occurrences[A](as: Seq[A]): Map[A, Int] =
  as.groupMapReduce(identity)(_ => 1)(_ + _)

Note: Even when applied to a view or a lazy collection it will always force the elements.

Definition Classes
IterableOps

def grouped(size: Int): Iterator[List[A]]

Partitions elements in fixed size iterable collections.

size

the number of elements per group

returns

An iterator producing iterable collections of size size, except the last will be less than size size if the elements don't divide evenly.

Definition Classes
IterableOps
See also

scala.collection.Iterator, method grouped

def hashCode(): Int

The hashCode method for reference types. See hashCode in scala.Any.

returns

the hash code value for this object.

Definition Classes
Seq → AnyRef → Any

Selects the first element of this iterable collection.

Note: might return different results for different runs, unless the underlying collection type is ordered.

returns

the first element of this iterable collection.

Definition Classes
IterableOps
Exceptions thrown

NoSuchElementException if the iterable collection is empty.

def headOption: Option[A]

Optionally selects the first element.

returns

the first element of this sequence if it is nonempty, None if it is empty.

Definition Classes
LinearSeqOpsIterableOps

def indexOf[B >: A](elem: B): Int

Finds index of first occurrence of some value in this sequence.

B

the type of the element elem.

elem

the element value to search for.

returns

the index >= 0 of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.

Definition Classes
SeqOps
Annotations
@deprecatedOverriding("Override indexOf(elem, from) instead - indexOf(elem) calls indexOf(elem, 0)", "2.13.0")

def indexOf[B >: A](elem: B, from: Int): Int

Finds index of first occurrence of some value in this sequence after or at some start index.

B

the type of the element elem.

elem

the element value to search for.

from

the start index

returns

the index >= from of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.

Definition Classes
SeqOps

def indexOfSlice[B >: A](that: collection.Seq[B]): Int

Finds first index where this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

that

the sequence to test

returns

the first index >= 0 such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.

Definition Classes
SeqOps
Annotations
@deprecatedOverriding("Override indexOfSlice(that, from) instead - indexOfSlice(that) calls indexOfSlice(that, 0)", "2.13.0")

def indexOfSlice[B >: A](that: collection.Seq[B], from: Int): Int

Finds first index after or at a start index where this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

that

the sequence to test

from

the start index

returns

the first index >= from such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.

Definition Classes
SeqOps

def indexWhere(p: (A) => Boolean, from: Int): Int

Finds index of the first element satisfying some predicate after or at some start index.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

from

the start index

returns

the index >= from of the first element of this sequence that satisfies the predicate p, or -1, if none exists.

Definition Classes
LinearSeqOpsSeqOps

def indexWhere(p: (A) => Boolean): Int

Finds index of the first element satisfying some predicate.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the index >= 0 of the first element of this sequence that satisfies the predicate p, or -1, if none exists.

Definition Classes
SeqOps
Annotations
@deprecatedOverriding("Override indexWhere(p, from) instead - indexWhere(p) calls indexWhere(p, 0)", "2.13.0")

def indices: Range

Produces the range of all indices of this sequence.

Note: Even when applied to a view or a lazy collection it will always force the elements.

returns

a Range value from 0 to one less than the length of this sequence.

Definition Classes
SeqOps

def init: List[A]

The initial part of the collection without its last element.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Definition Classes
IterableOps

def inits: Iterator[List[A]]

Iterates over the inits of this iterable collection. The first value will be this iterable collection and the final one will be an empty iterable collection, with the intervening values the results of successive applications of init.

Note: Even when applied to a view or a lazy collection it will always force the elements.

returns

an iterator over all the inits of this iterable collection

Definition Classes
IterableOps
Example:

    List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)

def intersect[B >: A](that: collection.Seq[B]): List[A]

Computes the multiset intersection between this sequence and another sequence.

that

the sequence of elements to intersect with.

returns

a new sequence which contains all elements of this sequence which also appear in that. If an element value x appears n times in that, then the first n occurrences of x will be retained in the result, but any following occurrences will be omitted.

Definition Classes
StrictOptimizedSeqOpsSeqOps

def isDefinedAt(x: Int): Boolean

Tests whether this sequence contains given index.

The implementations of methods apply and isDefinedAt turn a Seq[A] into a PartialFunction[Int, A].

returns

true if this sequence contains an element at position idx, false otherwise.

Definition Classes
LinearSeqOpsSeqOps

final def isEmpty: Boolean

Tests whether the list is empty.

Note: Implementations in subclasses that are not repeatedly traversable must take care not to consume any elements when isEmpty is called.

returns

true if the list contains no elements, false otherwise.

Definition Classes
ListLinearSeqOpsSeqOpsIterableOnceOps

final def isInstanceOf[T0]: Boolean

Test whether the dynamic type of the receiver object is T0.

Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

returns

true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any

def isTraversableAgain: Boolean

Tests whether this iterable collection can be repeatedly traversed. Always true for Iterables and false for Iterators unless overridden.

returns

true if it is repeatedly traversable, false otherwise.

Definition Classes
IterableOpsIterableOnceOps

def iterableFactory: SeqFactory[List]

The companion object of this list, providing various factory methods.

Definition Classes
ListLinearSeqLinearSeqSeqIterableSeqIterableIterableOps
Note

When implementing a custom collection type and refining CC to the new type, this method needs to be overridden to return a factory for the new type (the compiler will issue an error otherwise).

def iterator: Iterator[A]

Iterator can be used only once

Definition Classes
StrictOptimizedLinearSeqOpsLinearSeqOpsIterableOnce

def knownSize: Int

returns

The number of elements in this collection, if it can be cheaply computed, -1 otherwise. Cheaply usually means: Not requiring a collection traversal.

Definition Classes
IterableOnce

def last: A

Selects the last element.

returns

The last element of this list.

Definition Classes
ListLinearSeqOpsIterableOps
Exceptions thrown

NoSuchElementException If the list is empty.

def lastIndexOf[B >: A](elem: B, end: Int = length - 1): Int

Finds index of last occurrence of some value in this sequence before or at a given end index.

Note: will not terminate for infinite-sized collections.

B

the type of the element elem.

elem

the element value to search for.

end

the end index.

returns

the index <= end of the last element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.

Definition Classes
SeqOps

def lastIndexOfSlice[B >: A](that: collection.Seq[B]): Int

Finds last index where this sequence contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

that

the sequence to test

returns

the last index such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.

Definition Classes
SeqOps
Annotations
@deprecatedOverriding("Override lastIndexOfSlice(that, end) instead - lastIndexOfSlice(that) calls lastIndexOfSlice(that, Int.MaxValue)", "2.13.0")

def lastIndexOfSlice[B >: A](that: collection.Seq[B], end: Int): Int

Finds last index before or at a given end index where this sequence contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

that

the sequence to test

end

the end index

returns

the last index <= end such that the elements of this sequence starting at this index match the elements of sequence that, or -1 of no such subsequence exists.

Definition Classes
SeqOps

def lastIndexWhere(p: (A) => Boolean, end: Int): Int

Finds index of last element satisfying some predicate before or at given end index.

Note: will not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the index <= end of the last element of this sequence that satisfies the predicate p, or -1, if none exists.

Definition Classes
LinearSeqOpsSeqOps

def lastIndexWhere(p: (A) => Boolean): Int

Finds index of last element satisfying some predicate.

Note: will not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the index of the last element of this sequence that satisfies the predicate p, or -1, if none exists.

Definition Classes
SeqOps
Annotations
@deprecatedOverriding("Override lastIndexWhere(p, end) instead - lastIndexWhere(p) calls lastIndexWhere(p, Int.MaxValue)", "2.13.0")

def lastOption: Option[A]

Optionally selects the last element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

returns

the last element of this iterable collection$ if it is nonempty, None if it is empty.

Definition Classes
IterableOps

def lazyZip[B](that: collection.Iterable[B]): LazyZip2[A, B, List.this.type]

Analogous to zip except that the elements in each collection are not consumed until a strict operation is invoked on the returned LazyZip2 decorator.

Calls to lazyZip can be chained to support higher arities (up to 4) without incurring the expense of constructing and deconstructing intermediary tuples.

val xs = List(1, 2, 3)
val res = (xs lazyZip xs lazyZip xs lazyZip xs).map((a, b, c, d) => a + b + c + d)
// res == List(4, 8, 12)
B

the type of the second element in each eventual pair

that

the iterable providing the second element of each eventual pair

returns

a decorator LazyZip2 that allows strict operations to be performed on the lazily evaluated pairs or chained calls to lazyZip. Implicit conversion to Iterable[(A, B)] is also supported.

Definition Classes
Iterable

final def length: Int

The length (number of elements) of the list. size is an alias for length in Seq collections.

Definition Classes
ListLinearSeqOpsSeqOps

final def lengthCompare(len: Int): Int

Compares the length of this list to a test value.

len

the test value that gets compared with the length.

returns

A value x where

x <  0       if this.length <  len
x == 0       if this.length == len
x >  0       if this.length >  len

The method as implemented here does not call length directly; its running time is O(length min len) instead of O(length). The method should be overridden if computing length is cheap and knownSize returns -1.

Definition Classes
ListLinearSeqOpsSeqOps
See also

lengthIs

def lengthCompare(that: collection.Iterable[_]): Int

Compares the length of this sequence to the size of another Iterable.

that

the Iterable whose size is compared with this sequence's length.

returns

A value x where

x <  0       if this.length <  that.size
x == 0       if this.length == that.size
x >  0       if this.length >  that.size

The method as implemented here does not call length or size directly; its running time is O(this.length min that.size) instead of O(this.length + that.size). The method should be overridden if computing size is cheap and knownSize returns -1.

Definition Classes
LinearSeqOpsSeqOps

final def lengthIs: SizeCompareOps

Returns a value class containing operations for comparing the length of this sequence to a test value.

These operations are implemented in terms of lengthCompare(Int), and allow the following more readable usages:

this.lengthIs < len     // this.lengthCompare(len) < 0
this.lengthIs <= len    // this.lengthCompare(len) <= 0
this.lengthIs == len    // this.lengthCompare(len) == 0
this.lengthIs != len    // this.lengthCompare(len) != 0
this.lengthIs >= len    // this.lengthCompare(len) >= 0
this.lengthIs > len     // this.lengthCompare(len) > 0
Definition Classes
SeqOps
Annotations
@inline()

def lift: (Int) => Option[A]

Turns this partial function into a plain function returning an Option result.

returns

a function that takes an argument x to Some(this(x)) if this is defined for x, and to None otherwise.

Definition Classes
PartialFunction
See also

Function.unlift

final def map[B](f: (A) => B): List[B]

Builds a new list by applying a function to all elements of this list.

B

the element type of the returned list.

f

the function to apply to each element.

returns

a new list resulting from applying the given function f to each element of this list and collecting the results.

Definition Classes
ListStrictOptimizedIterableOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

final def mapConserve[B >: A <: AnyRef](f: (A) => B): List[B]

Builds a new list by applying a function to all elements of this list. Like xs map f, but returns xs unchanged if function f maps all elements to themselves (as determined by eq).

B

the element type of the returned collection.

f

the function to apply to each element.

returns

a list resulting from applying the given function f to each element of this list and collecting the results.

Annotations
@inline()

def max[B >: A](implicit ord: math.Ordering[B]): A

Finds the largest element.

B

The type over which the ordering is defined.

ord

An ordering to be used for comparing elements.

returns

the largest element of this collection with respect to the ordering ord.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def maxBy[B](f: (A) => B)(implicit cmp: math.Ordering[B]): A

Finds the first element which yields the largest value measured by function f.

B

The result type of the function f.

f

The measuring function.

cmp

An ordering to be used for comparing elements.

returns

the first element of this collection with the largest value measured by function f with respect to the ordering cmp.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def maxByOption[B](f: (A) => B)(implicit cmp: math.Ordering[B]): Option[A]

Finds the first element which yields the largest value measured by function f.

B

The result type of the function f.

f

The measuring function.

cmp

An ordering to be used for comparing elements.

returns

an option value containing the first element of this collection with the largest value measured by function f with respect to the ordering cmp.

Definition Classes
IterableOnceOps

def maxOption[B >: A](implicit ord: math.Ordering[B]): Option[A]

Finds the largest element.

B

The type over which the ordering is defined.

ord

An ordering to be used for comparing elements.

returns

an option value containing the largest element of this collection with respect to the ordering ord.

Definition Classes
IterableOnceOps

def min[B >: A](implicit ord: math.Ordering[B]): A

Finds the smallest element.

B

The type over which the ordering is defined.

ord

An ordering to be used for comparing elements.

returns

the smallest element of this collection with respect to the ordering ord.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def minBy[B](f: (A) => B)(implicit cmp: math.Ordering[B]): A

Finds the first element which yields the smallest value measured by function f.

B

The result type of the function f.

f

The measuring function.

cmp

An ordering to be used for comparing elements.

returns

the first element of this collection with the smallest value measured by function f with respect to the ordering cmp.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def minByOption[B](f: (A) => B)(implicit cmp: math.Ordering[B]): Option[A]

Finds the first element which yields the smallest value measured by function f.

B

The result type of the function f.

f

The measuring function.

cmp

An ordering to be used for comparing elements.

returns

an option value containing the first element of this collection with the smallest value measured by function f with respect to the ordering cmp.

Definition Classes
IterableOnceOps

def minOption[B >: A](implicit ord: math.Ordering[B]): Option[A]

Finds the smallest element.

B

The type over which the ordering is defined.

ord

An ordering to be used for comparing elements.

returns

an option value containing the smallest element of this collection with respect to the ordering ord.

Definition Classes
IterableOnceOps

final def mkString: String

Displays all elements of this collection in a string.

Delegates to addString, which can be overridden.

returns

a string representation of this collection. In the resulting string the string representations (w.r.t. the method toString) of all elements of this collection follow each other without any separator string.

Definition Classes
IterableOnceOps
Annotations
@inline()

final def mkString(sep: String): String

Displays all elements of this collection in a string using a separator string.

Delegates to addString, which can be overridden.

sep

the separator string.

returns

a string representation of this collection. In the resulting string the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.

Definition Classes
IterableOnceOps
Annotations
@inline()
Example:

    List(1, 2, 3).mkString("|") = "1|2|3"

final def mkString(start: String, sep: String, end: String): String

Displays all elements of this collection in a string using start, end, and separator strings.

Delegates to addString, which can be overridden.

start

the starting string.

sep

the separator string.

end

the ending string.

returns

a string representation of this collection. The resulting string begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.

Definition Classes
IterableOnceOps
Example:

    List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def newSpecificBuilder: Builder[A, List[A]]

returns

a strict builder for the same collection type. Note that in the case of lazy collections (e.g. View or immutable.LazyList), it is possible to implement this method but the resulting Builder will break laziness. As a consequence, operations should preferably be implemented with fromSpecific instead of this method.

Attributes
protected
Definition Classes
IterableFactoryDefaultsIterableOps
Note

When implementing a custom collection type and refining C to the new type, this method needs to be overridden (the compiler will issue an error otherwise). In the common case where C =:= CC[A], this can be done by mixing in the IterableFactoryDefaults trait, which implements the method using iterableFactory.

,

As witnessed by the @uncheckedVariance annotation, using this method might be unsound. However, as long as the returned builder is only fed with A values taken from this instance, it is safe.

def nonEmpty: Boolean

Tests whether the collection is not empty.

returns

true if the collection contains at least one element, false otherwise.

Definition Classes
IterableOnceOps
Annotations
@deprecatedOverriding("nonEmpty is defined as !isEmpty; override isEmpty instead", "2.13.0")

final def notify(): Unit

Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def notifyAll(): Unit

Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

def occCounts[B](sq: collection.Seq[B]): mutable.Map[B, Int]

Attributes
protected[scala.collection]
Definition Classes
SeqOps

def orElse[A1 <: Int, B1 >: A](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

A1

the argument type of the fallback function

B1

the result type of the fallback function

that

the fallback function

returns

a partial function which has as domain the union of the domains of this partial function and that. The resulting partial function takes x to this(x) where this is defined, and to that(x) where it is not.

Definition Classes
PartialFunction

def padTo[B >: A](len: Int, elem: B): List[B]

A copy of this sequence with an element value appended until a given target length is reached.

B

the element type of the returned sequence.

len

the target length

elem

the padding value

returns

a new sequence consisting of all elements of this sequence followed by the minimal number of occurrences of elem so that the resulting collection has a length of at least len.

Definition Classes
StrictOptimizedSeqOpsSeqOps

def partition(p: (A) => Boolean): (List[A], List[A])

A pair of, first, all elements that satisfy predicate p and, second, all elements that do not. Interesting because it splits a collection in two.

The default implementation provided here needs to traverse the collection twice. Strict collections have an overridden version of partition in StrictOptimizedIterableOps, which requires only a single traversal.

Definition Classes
StrictOptimizedIterableOpsIterableOps

def partitionMap[A1, A2](f: (A) => Either[A1, A2]): (List[A1], List[A2])

Applies a function f to each element of the iterable collection and returns a pair of iterable collections: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.

Example:

val xs = Iterable(1, "one", 2, "two", 3, "three") partitionMap {
 case i: Int => Left(i)
 case s: String => Right(s)
}
// xs == (Iterable(1, 2, 3),
//        Iterable(one, two, three))
A1

the element type of the first resulting collection

A2

the element type of the second resulting collection

f

the 'split function' mapping the elements of this iterable collection to an scala.util.Either

returns

a pair of iterable collections: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.

Definition Classes
StrictOptimizedIterableOpsIterableOps

def patch[B >: A](from: Int, other: IterableOnce[B], replaced: Int): List[B]

Produces a new immutable sequence where a slice of elements in this immutable sequence is replaced by another sequence.

Patching at negative indices is the same as patching starting at 0. Patching at indices at or larger than the length of the original immutable sequence appends the patch to the end. If more values are replaced than actually exist, the excess is ignored.

B

the element type of the returned immutable sequence.

from

the index of the first replaced element

other

the replacement sequence

replaced

the number of elements to drop in the original immutable sequence

returns

a new immutable sequence consisting of all elements of this immutable sequence except that replaced elements starting from from are replaced by all the elements of other.

Definition Classes
StrictOptimizedSeqOpsSeqOps

def permutations: Iterator[List[A]]

Iterates over distinct permutations.

Note: Even when applied to a view or a lazy collection it will always force the elements.

returns

An Iterator which traverses the distinct permutations of this sequence.

Definition Classes
SeqOps
Example:

    "abb".permutations = Iterator(abb, bab, bba)

def prepended[B >: A](elem: B): List[B]

A copy of the list with an element prepended.

Also, the original list is not modified, so you will want to capture the result.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = 2 +: x
y: List[Int] = List(2, 1)

scala> println(x)
List(1)
B

the element type of the returned list.

elem

the prepended element

returns

a new list consisting of value followed by all elements of this list.

Definition Classes
ListStrictOptimizedSeqOpsSeqOps

def prependedAll[B >: A](prefix: IterableOnce[B]): List[B]

As with :++, returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from :++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

B

the element type of the returned collection.

prefix

the iterable to prepend.

returns

a new list which contains all elements of prefix followed by all the elements of this list.

Definition Classes
ListStrictOptimizedSeqOpsSeqOps

def product[B >: A](implicit num: math.Numeric[B]): B

Multiplies up the elements of this collection.

B

the result type of the * operator.

num

an implicit parameter defining a set of numeric operations which includes the * operator to be used in forming the product.

returns

the product of all elements of this collection with respect to the * operator in num.

Definition Classes
IterableOnceOps

def reduce[B >: A](op: (B, B) => B): B

Reduces the elements of this collection using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

B

A type parameter for the binary operator, a supertype of A.

op

A binary operator that must be associative.

returns

The result of applying reduce operator op between all the elements if the collection is nonempty.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def reduceLeft[B >: A](op: (B, A) => B): B

Applies a binary operator to all elements of this collection, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

B

the result type of the binary operator.

op

the binary operator.

returns

the result of inserting op between consecutive elements of this collection, going left to right:

op( op( ... op(x_1, x_2) ..., x_{n-1}), x_n)

where x1, ..., xn are the elements of this collection.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def reduceLeftOption[B >: A](op: (B, A) => B): Option[B]

Optionally applies a binary operator to all elements of this collection, going left to right.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

B

the result type of the binary operator.

op

the binary operator.

returns

an option value containing the result of reduceLeft(op) if this collection is nonempty, None otherwise.

Definition Classes
IterableOnceOps

def reduceOption[B >: A](op: (B, B) => B): Option[B]

Reduces the elements of this collection, if any, using the specified associative binary operator.

The order in which operations are performed on elements is unspecified and may be nondeterministic.

B

A type parameter for the binary operator, a supertype of A.

op

A binary operator that must be associative.

returns

An option value containing result of applying reduce operator op between all the elements if the collection is nonempty, and None otherwise.

Definition Classes
IterableOnceOps

def reduceRight[B >: A](op: (A, B) => B): B

Applies a binary operator to all elements of this collection, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

B

the result type of the binary operator.

op

the binary operator.

returns

the result of inserting op between consecutive elements of this collection, going right to left:

op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))

where x1, ..., xn are the elements of this collection.

Definition Classes
IterableOnceOps
Exceptions thrown

UnsupportedOperationException if this collection is empty.

def reduceRightOption[B >: A](op: (A, B) => B): Option[B]

Optionally applies a binary operator to all elements of this collection, going right to left.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

B

the result type of the binary operator.

op

the binary operator.

returns

an option value containing the result of reduceRight(op) if this collection is nonempty, None otherwise.

Definition Classes
IterableOnceOps

final def reverse: List[A]

Returns new list with elements in reversed order.

Note: Even when applied to a view or a lazy collection it will always force the elements.

returns

A new list with all elements of this list in reversed order.

Definition Classes
ListSeqOps

def reverseIterator: Iterator[A]

An iterator yielding elements in reversed order.

Note: will not terminate for infinite-sized collections.

Note: xs.reverseIterator is the same as xs.reverse.iterator but might be more efficient.

returns

an iterator yielding the elements of this sequence in reversed order

Definition Classes
SeqOps

def reverse_:::[B >: A](prefix: List[B]): List[B]

Adds the elements of a given list in reverse order in front of this list. xs reverse_::: ys is equivalent to xs.reverse ::: ys but is more efficient.

prefix

the prefix to reverse and then prepend

returns

the concatenation of the reversed prefix and the current list.

def reversed: collection.Iterable[A]

Attributes
protected
Definition Classes
IterableOnceOps

def runWith[U](action: (A) => U): (Int) => Boolean

Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.

Note that expression pf.runWith(action)(x) is equivalent to

if(pf isDefinedAt x) { action(pf(x)); true } else false

except that runWith is implemented via applyOrElse and thus potentially more efficient. Using runWith avoids double evaluation of pattern matchers and guards for partial function literals.

action

the action function

returns

a function which maps arguments x to isDefinedAt(x). The resulting function runs action(this(x)) where this is defined.

Definition Classes
PartialFunction
Since

2.10

See also

applyOrElse.

def sameElements[B >: A](that: IterableOnce[B]): Boolean

Are the elements of this collection the same (and in the same order) as those of that?

Definition Classes
LinearSeqOpsSeqOps

def scan[B >: A](z: B)(op: (B, B) => B): List[B]

Computes a prefix scan of the elements of the collection.

Note: The neutral element z may be applied more than once.

B

element type of the resulting collection

z

neutral element for the operator op

op

the associative operator for the scan

returns

a new iterable collection containing the prefix scan of the elements in this iterable collection

Definition Classes
IterableOps

def scanLeft[B](z: B)(op: (B, A) => B): List[B]

Produces a iterable collection containing cumulative results of applying the operator going left to right, including the initial value.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

B

the type of the elements in the resulting collection

z

the initial value

op

the binary operator applied to the intermediate result and the element

returns

collection with intermediate results

Definition Classes
StrictOptimizedIterableOpsIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def scanRight[B](z: B)(op: (A, B) => B): List[B]

Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Example:

List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
B

the type of the elements in the resulting collection

z

the initial value

op

the binary operator applied to the intermediate result and the element

returns

collection with intermediate results

Definition Classes
IterableOps

Search within an interval in this sorted sequence for a specific element. If this sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.

The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.

elem

the element to find.

from

the index where the search starts.

to

the index following where the search ends.

ord

the ordering to be used to compare elements.

returns

a Found value containing the index corresponding to the element in the sequence, or the InsertionPoint where the element would be inserted if the element is not in the sequence.

Definition Classes
SeqOps
Note

if to <= from, the search space is empty, and an InsertionPoint at from is returned

See also

scala.collection.IndexedSeq

scala.math.Ordering

scala.collection.SeqOps, method sorted

Search this sorted sequence for a specific element. If the sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.

The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.

elem

the element to find.

ord

the ordering to be used to compare elements.

returns

a Found value containing the index corresponding to the element in the sequence, or the InsertionPoint where the element would be inserted if the element is not in the sequence.

Definition Classes
SeqOps
See also

scala.collection.IndexedSeq

scala.math.Ordering

scala.collection.SeqOps, method sorted

def segmentLength(p: (A) => Boolean, from: Int): Int

Computes length of longest segment whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

from

the index where the search starts.

returns

the length of the longest segment of this sequence starting from index from such that every element of the segment satisfies the predicate p.

Definition Classes
LinearSeqOpsSeqOps

final def segmentLength(p: (A) => Boolean): Int

Computes length of longest segment whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

p

the predicate used to test elements.

returns

the length of the longest segment of this sequence such that every element of the segment satisfies the predicate p.

Definition Classes
SeqOps

final def size: Int

The size of this sequence.

Note: will not terminate for infinite-sized collections.

returns

the number of elements in this sequence.

Definition Classes
SeqOpsIterableOnceOps

final def sizeCompare(that: collection.Iterable[_]): Int

Compares the size of this sequence to the size of another Iterable.

that

the Iterable whose size is compared with this sequence's size.

returns

A value x where

x <  0       if this.size <  that.size
x == 0       if this.size == that.size
x >  0       if this.size >  that.size

The method as implemented here does not call size directly; its running time is O(this.size min that.size) instead of O(this.size + that.size). The method should be overridden if computing size is cheap and knownSize returns -1.

Definition Classes
SeqOpsIterableOps

final def sizeCompare(otherSize: Int): Int

Compares the size of this sequence to a test value.

otherSize

the test value that gets compared with the size.

returns

A value x where

x <  0       if this.size <  otherSize
x == 0       if this.size == otherSize
x >  0       if this.size >  otherSize

The method as implemented here does not call size directly; its running time is O(size min otherSize) instead of O(size). The method should be overridden if computing size is cheap and knownSize returns -1.

Definition Classes
SeqOpsIterableOps
See also

sizeIs

final def sizeIs: SizeCompareOps

Returns a value class containing operations for comparing the size of this iterable collection to a test value.

These operations are implemented in terms of sizeCompare(Int), and allow the following more readable usages:

this.sizeIs < size     // this.sizeCompare(size) < 0
this.sizeIs <= size    // this.sizeCompare(size) <= 0
this.sizeIs == size    // this.sizeCompare(size) == 0
this.sizeIs != size    // this.sizeCompare(size) != 0
this.sizeIs >= size    // this.sizeCompare(size) >= 0
this.sizeIs > size     // this.sizeCompare(size) > 0
Definition Classes
IterableOps
Annotations
@inline()

def slice(from: Int, until: Int): List[A]

from

the lowest index to include from this list.

until

the lowest index to EXCLUDE from this list.

returns

a list containing the elements greater than or equal to index from extending up to (but not including) index until of this list.

Definition Classes
ListIterableOpsIterableOnceOps
Example:
    // Given a list
    val letters = List('a','b','c','d','e')
    
    // `slice` returns all elements beginning at index `from` and afterwards,
    // up until index `until` (excluding index `until`.)
    letters.slice(1,3) // Returns List('b','c')

def sliding(size: Int, step: Int): Iterator[List[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

size

the number of elements per group

step

the distance between the first elements of successive groups

returns

An iterator producing iterable collections of size size, except the last element (which may be the only element) will be truncated if there are fewer than size elements remaining to be grouped.

Definition Classes
IterableOps
See also

scala.collection.Iterator, method sliding

def sliding(size: Int): Iterator[List[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.) The "sliding window" step is set to one.

size

the number of elements per group

returns

An iterator producing iterable collections of size size, except the last element (which may be the only element) will be truncated if there are fewer than size elements remaining to be grouped.

Definition Classes
IterableOps
See also

scala.collection.Iterator, method sliding

def sortBy[B](f: (A) => B)(implicit ord: Ordering[B]): List[A]

Sorts this sequence according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.

B

the target type of the transformation f, and the type where the ordering ord is defined.

f

the transformation function mapping elements to some other domain B.

ord

the ordering assumed on domain B.

returns

a sequence consisting of the elements of this sequence sorted according to the ordering where x < y if ord.lt(f(x), f(y)).

Definition Classes
SeqOps
Example:
    val words = "The quick brown fox jumped over the lazy dog".split(' ')
    // this works because scala.Ordering will implicitly provide an Ordering[Tuple2[Int, Char]]
    words.sortBy(x => (x.length, x.head))
    res0: Array[String] = Array(The, dog, fox, the, lazy, over, brown, quick, jumped)
See also

scala.math.Ordering

def sortWith(lt: (A, A) => Boolean): List[A]

Sorts this sequence according to a comparison function.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

The sort is stable. That is, elements that are equal (as determined by lt) appear in the same order in the sorted sequence as in the original.

lt

the comparison function which tests whether its first argument precedes its second argument in the desired ordering.

returns

a sequence consisting of the elements of this sequence sorted according to the comparison function lt.

Definition Classes
SeqOps
Example:
    List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) =
    List("Bob", "John", "Steve", "Tom")

def sorted[B >: A](implicit ord: Ordering[B]): List[A]

Sorts this immutable sequence according to an Ordering.

The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.

ord

the ordering to be used to compare elements.

returns

a immutable sequence consisting of the elements of this immutable sequence sorted according to the ordering ord.

Definition Classes
StrictOptimizedSeqOpsSeqOps
See also

scala.math.Ordering Note: Even when applied to a view or a lazy collection it will always force the elements.

final def span(p: (A) => Boolean): (List[A], List[A])

Splits this list into a prefix/suffix pair according to a predicate.

Note: c span p is equivalent to (but possibly more efficient than) (c takeWhile p, c dropWhile p), provided the evaluation of the predicate p does not cause any side-effects.

p

the test predicate

returns

a pair consisting of the longest prefix of this list whose elements all satisfy p, and the rest of this list.

Definition Classes
ListStrictOptimizedIterableOpsIterableOpsIterableOnceOps
Annotations
@inline()
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterators that were returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterators as well.

def splitAt(n: Int): (List[A], List[A])

Splits this list into a prefix/suffix pair at a given position.

Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n).

n

the position at which to split.

returns

a pair of lists consisting of the first n elements of this list, and the other elements.

Definition Classes
ListIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterators that were returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterators as well.

def startsWith[B >: A](that: IterableOnce[B], offset: Int = 0): Boolean

Tests whether this sequence contains the given sequence at a given index.

Note: If the both the receiver object this and the argument that are infinite sequences this method may not terminate.

that

the sequence to test

offset

the index where the sequence is searched.

returns

true if the sequence that is contained in this sequence at index offset, otherwise false.

Definition Classes
SeqOps

def stepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S

Returns a Stepper for the elements of this collection.

The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.

The implicit StepperShape parameter defines the resulting Stepper type according to the element type of this collection.

    For collections of Int, Short, Byte or Char, an IntStepper is returnedFor collections of Double or Float, a DoubleStepper is returnedFor collections of Long a LongStepper is returnedFor any other element type, an AnyStepper is returned

Note that this method is overridden in subclasses and the return type is refined to S with EfficientSplit, for example IndexedSeqOps.stepper. For Steppers marked with scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters allow creating parallel streams, whereas bare Steppers can be converted only to sequential streams.

Definition Classes
IterableOnce

final def strictOptimizedCollect[B, C2](b: Builder[B, C2], pf: PartialFunction[A, B]): C2

B

Type of elements of the resulting collection (e.g. String)

C2

Type of the resulting collection (e.g. List[String])

b

Builder to use to build the resulting collection

pf

Element transformation partial function

returns

The resulting collection

Attributes
protected[this]
Definition Classes
StrictOptimizedIterableOps
Annotations
@inline()

final def strictOptimizedConcat[B >: A, C2](that: IterableOnce[B], b: Builder[B, C2]): C2

B

Type of elements of the resulting collections (e.g. Int)

C2

Type of the resulting collection (e.g. List[Int])

that

Elements to concatenate to this collection

b

Builder to use to build the resulting collection

returns

The resulting collection

Attributes
protected[this]
Definition Classes
StrictOptimizedIterableOps
Annotations
@inline()

final def strictOptimizedFlatMap[B, C2](b: Builder[B, C2], f: (A) => IterableOnce[B]): C2

B

Type of elements of the resulting collection (e.g. String)

C2

Type of the resulting collection (e.g. List[String])

b

Builder to use to build the resulting collection

f

Element transformation function

returns

The resulting collection

Attributes
protected[this]
Definition Classes
StrictOptimizedIterableOps
Annotations
@inline()

final def strictOptimizedFlatten[B, C2](b: Builder[B, C2])(implicit toIterableOnce: (A) => IterableOnce[B]): C2

B

Type of elements of the resulting collection (e.g. Int)

C2

Type of the resulting collection (e.g. List[Int])

b

Builder to use to build the resulting collection

toIterableOnce

Evidence that A can be seen as an IterableOnce[B]

returns

The resulting collection

Attributes
protected[this]
Definition Classes
StrictOptimizedIterableOps
Annotations
@inline()

final def strictOptimizedMap[B, C2](b: Builder[B, C2], f: (A) => B): C2

B

Type of elements of the resulting collection (e.g. String)

C2

Type of the resulting collection (e.g. List[String])

b

Builder to use to build the resulting collection

f

Element transformation function

returns

The resulting collection

Attributes
protected[this]
Definition Classes
StrictOptimizedIterableOps
Annotations
@inline()

final def strictOptimizedZip[B, C2](that: IterableOnce[B], b: Builder[(A, B), C2]): C2

B

Type of elements of the second collection (e.g. String)

C2

Type of the resulting collection (e.g. List[(Int, String)])

that

Collection to zip with this collection

b

Builder to use to build the resulting collection

returns

The resulting collection

Attributes
protected[this]
Definition Classes
StrictOptimizedIterableOps
Annotations
@inline()

def stringPrefix: String

Attributes
protected[this]
Definition Classes
LinearSeqSeqIterable
Annotations
@deprecatedOverriding("Compatibility override", "2.13.0")

def sum[B >: A](implicit num: math.Numeric[B]): B

Sums up the elements of this collection.

B

the result type of the + operator.

num

an implicit parameter defining a set of numeric operations which includes the + operator to be used in forming the sum.

returns

the sum of all elements of this collection with respect to the + operator in num.

Definition Classes
IterableOnceOps

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def tail: List[A]

The rest of the collection without its first element.

Definition Classes
IterableOps

def tails: Iterator[List[A]]

Iterates over the tails of this sequence. The first value will be this sequence and the final one will be an empty sequence, with the intervening values the results of successive applications of tail.

returns

an iterator over all the tails of this sequence

Definition Classes
LinearSeqOpsIterableOps
Example:

    List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)

def take(n: Int): List[A]

Selects the first n elements.

n

the number of elements to take from this list.

returns

a list consisting only of the first n elements of this list, or else the whole list, if it has less than n elements. If n is negative, returns an empty list.

Definition Classes
ListIterableOpsIterableOnceOps
Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

def takeRight(n: Int): List[A]

A collection containing the last n elements of this collection.

Note: Even when applied to a view or a lazy collection it will always force the elements.

n

the number of elements to take from this list.

returns

a list consisting only of the last n elements of this list, or else the whole list, if it has less than n elements. If n is negative, returns an empty list.

Definition Classes
ListStrictOptimizedIterableOpsIterableOps

final def takeWhile(p: (A) => Boolean): List[A]

Takes longest prefix of elements that satisfy a predicate.

p

The predicate used to test elements.

returns

the longest prefix of this list whose elements all satisfy the predicate p.

Definition Classes
ListIterableOpsIterableOnceOps
Annotations
@inline()

def tapEach[U](f: (A) => U): List[A]

Applies a side-effecting function to each element in this collection. Strict collections will apply f to their elements immediately, while lazy collections like Views and LazyLists will only apply f on each element if and when that element is evaluated, and each time that element is evaluated.

U

the return type of f

f

a function to apply to each element in this iterable collection

returns

The same logical collection as this

Definition Classes
StrictOptimizedIterableOpsIterableOpsIterableOnceOps

def to[C1](factory: Factory[A, C1]): C1

Given a collection factory factory, convert this collection to the appropriate representation for the current element type A. Example uses:

xs.to(List) xs.to(ArrayBuffer) xs.to(BitSet) // for xs: Iterable[Int]

Definition Classes
IterableOnceOps

def toArray[B >: A](implicit arg0: ClassTag[B]): Array[B]

Convert collection to array.

Definition Classes
IterableOnceOps

final def toBuffer[B >: A]: Buffer[B]

Definition Classes
IterableOnceOps
Annotations
@inline()

def toIndexedSeq: IndexedSeq[A]

Definition Classes
IterableOnceOps

final def toIterable: List.this.type

returns

This collection as an Iterable[A]. No new collection will be built if this is already an Iterable[A].

Definition Classes
IterableIterableOps

final def toList: List[A]

Definition Classes
ListIterableOnceOps

def toMap[K, V](implicit ev: <:<[A, (K, V)]): Map[K, V]

Definition Classes
IterableOnceOps

final def toSeq: List.this.type

returns

This collection as a Seq[A]. This is equivalent to to(Seq) but might be faster.

Definition Classes
SeqIterableOnceOps

def toSet[B >: A]: Set[B]

Definition Classes
IterableOnceOps

def toString(): String

Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

returns

a String representation of the object.

Definition Classes
SeqFunction1Iterable → AnyRef → Any

def toVector: Vector[A]

Definition Classes
IterableOnceOps

def transpose[B](implicit asIterable: (A) => collection.Iterable[B]): List[List[B]]

Transposes this iterable collection of iterable collections into a iterable collection of iterable collections.

The resulting collection's type will be guided by the static type of iterable collection. For example:

val xs = List(
           Set(1, 2, 3),
           Set(4, 5, 6)).transpose
// xs == List(
//         List(1, 4),
//         List(2, 5),
//         List(3, 6))

val ys = Vector(
           List(1, 2, 3),
           List(4, 5, 6)).transpose
// ys == Vector(
//         Vector(1, 4),
//         Vector(2, 5),
//         Vector(3, 6))

Note: Even when applied to a view or a lazy collection it will always force the elements.

B

the type of the elements of each iterable collection.

asIterable

an implicit conversion which asserts that the element type of this iterable collection is an Iterable.

returns

a two-dimensional iterable collection of iterable collections which has as nth row the nth column of this iterable collection.

Definition Classes
IterableOps
Exceptions thrown

IllegalArgumentException if all collections in this iterable collection are not of the same size.

def unapply(a: Int): Option[A]

Tries to extract a B from an A in a pattern matching expression.

Definition Classes
PartialFunction

def unlift: PartialFunction[Int, B]

Converts an optional function to a partial function.

Implicit
This member is added by an implicit conversion from List[A] toUnliftOps[Int, B] performed by method UnliftOps in scala.Function1.This conversion will take place only if A is a subclass of Option[B] (A <: Option[B]).
Definition Classes
UnliftOps
Example:

    Unlike Function.unlift, this UnliftOps.unlift method can be used in extractors.

    val of: Int => Option[String] = { i =>
      if (i == 2) {
        Some("matched by an optional function")
      } else {
        None
      }
    }
    
    util.Random.nextInt(4) match {
      case of.unlift(m) => // Convert an optional function to a pattern
        println(m)
      case _ =>
        println("Not matched")
    }

def unzip[A1, A2](implicit asPair: (A) => (A1, A2)): (List[A1], List[A2])

Converts this iterable collection of pairs into two collections of the first and second half of each pair.

val xs = Iterable(
           (1, "one"),
           (2, "two"),
           (3, "three")).unzip
// xs == (Iterable(1, 2, 3),
//        Iterable(one, two, three))
A1

the type of the first half of the element pairs

A2

the type of the second half of the element pairs

asPair

an implicit conversion which asserts that the element type of this iterable collection is a pair.

returns

a pair of iterable collections, containing the first, respectively second half of each element pair of this iterable collection.

Definition Classes
StrictOptimizedIterableOpsIterableOps

def unzip3[A1, A2, A3](implicit asTriple: (A) => (A1, A2, A3)): (List[A1], List[A2], List[A3])

Converts this iterable collection of triples into three collections of the first, second, and third element of each triple.

val xs = Iterable(
           (1, "one", '1'),
           (2, "two", '2'),
           (3, "three", '3')).unzip3
// xs == (Iterable(1, 2, 3),
//        Iterable(one, two, three),
//        Iterable(1, 2, 3))
A1

the type of the first member of the element triples

A2

the type of the second member of the element triples

A3

the type of the third member of the element triples

asTriple

an implicit conversion which asserts that the element type of this iterable collection is a triple.

returns

a triple of iterable collections, containing the first, second, respectively third member of each element triple of this iterable collection.

Definition Classes
StrictOptimizedIterableOpsIterableOps

def updated[B >: A](index: Int, elem: B): List[B]

A copy of this list with one single replaced element.

B

the element type of the returned list.

index

the position of the replacement

elem

the replacing element

returns

a new list which is a copy of this list with the element at position index replaced by elem.

Definition Classes
ListStrictOptimizedSeqOpsSeqOps
Exceptions thrown

IndexOutOfBoundsException if index does not satisfy 0 <= index < length. In case of a lazy collection this exception may be thrown at a later time or not at all (if the end of the collection is never evaluated).

def view: SeqView[A]

A view over the elements of this collection.

Definition Classes
SeqOpsIterableOps

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

def withFilter(p: (A) => Boolean): WithFilter[A, [_]List[_]]

Creates a non-strict filter of this iterable collection.

Note: the difference between c filter p and c withFilter p is that the former creates a new collection, whereas the latter only restricts the domain of subsequent map, flatMap, foreach, and withFilter operations.

Note: might return different results for different runs, unless the underlying collection type is ordered.

p

the predicate used to test elements.

returns

an object of class WithFilter, which supports map, flatMap, foreach, and withFilter operations. All these operations apply to those elements of this iterable collection which satisfy the predicate p.

Definition Classes
IterableOps

def writeReplace(): AnyRef

Attributes
protected[this]
Definition Classes
DefaultSerializable

def zip[B](that: IterableOnce[B]): List[(A, B)]

Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.

B

the type of the second half of the returned pairs

that

The iterable providing the second half of each result pair

returns

a new iterable collection containing pairs consisting of corresponding elements of this iterable collection and that. The length of the returned collection is the minimum of the lengths of this iterable collection and that.

Definition Classes
StrictOptimizedIterableOpsIterableOps

def zipAll[A1 >: A, B](that: collection.Iterable[B], thisElem: A1, thatElem: B): List[(A1, B)]

Returns a iterable collection formed from this iterable collection and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

that

the iterable providing the second half of each result pair

thisElem

the element to be used to fill up the result if this iterable collection is shorter than that.

thatElem

the element to be used to fill up the result if that is shorter than this iterable collection.

returns

a new collection of type That containing pairs consisting of corresponding elements of this iterable collection and that. The length of the returned collection is the maximum of the lengths of this iterable collection and that. If this iterable collection is shorter than that, thisElem values are used to pad the result. If that is shorter than this iterable collection, thatElem values are used to pad the result.

Definition Classes
IterableOps

def zipWithIndex: List[(A, Int)]

Zips this iterable collection with its indices.

returns

A new iterable collection containing pairs consisting of all elements of this iterable collection paired with their index. Indices start at 0.

Definition Classes
StrictOptimizedIterableOpsIterableOpsIterableOnceOps
Example:

    List("a", "b", "c").zipWithIndex == List(("a", 0), ("b", 1), ("c", 2))

Note

Reuse: After calling this method, one should discard the iterator it was called on, and use only the iterator that was returned. Using the old iterator is undefined, subject to change, and may result in changes to the new iterator as well.

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/collection/immutable/List.html