A class supporting filtered operations. Instances of this class are returned by method withFilter.
The type implementing this traversable
Is the tail of this stream defined?
Test two objects for inequality.
true if !(this == that), false otherwise.
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.
a hash value consistent with ==
Construct a stream consisting of a given first element followed by elements from a lazily evaluated Stream.
Construct a stream consisting of the concatenation of the given stream and a lazily evaluated Stream.
Create a new stream which contains all elements of this stream followed by all elements of Traversable that.
The element type of the returned collection.That
the class of the returned collection. Where possible, That is the same class as the current collection class Repr, but this depends on the element type B being admissible for that class, which means that an implicit instance of type CanBuildFrom[Repr, B, That] is found.
The scala.collection.GenTraversableOnce to be concatenated to this Stream.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
A new collection containing the result of concatenating this with that.
It's subtle why this works. We know that if the target type of the scala.collection.mutable.Builder That is either a Stream, or one of its supertypes, or undefined, then StreamBuilder will be chosen for the implicit. We recognize that fact and optimize to get more laziness.
This method doesn't cause the Stream to be fully realized but it should be noted that using the ++ operator from another collection type could cause infinite realization of a Stream. For example, referring to the definition of fibs in the preamble, the following would never return: List(BigInt(12)) ++ fibs.
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.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = LinkedList(2) y: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val z = x ++: y z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
This overload exists because: for the implementation of ++: we should reuse that of ++ because many collections override it with more efficient versions.
Since TraversableOnce has no ++ method, we have to implement that directly, but Traversable and down can use the overload.
the element type of the returned collection.
the class of the returned collection. Where possible, That is the same class as the current collection class Repr, but this depends on the element type B being admissible for that class, which means that an implicit instance of type CanBuildFrom[Repr, B, That] is found.
the traversable to append.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
a new collection of type That which contains all elements of this traversable collection followed by all elements of that.
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.
Example:
scala> val x = List(1) x: List[Int] = List(1) scala> val y = LinkedList(2) y: scala.collection.mutable.LinkedList[Int] = LinkedList(2) scala> val z = x ++: y z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
the element type of the returned collection.
the traversable to append.
a new stream which contains all elements of this stream followed by all elements of that.
A copy of the stream with an element prepended.
Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.
Also, the original stream 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)
the prepended element
a new stream consisting of elem followed by all elements of this stream.
Applies a binary operator to a start value and all elements of this traversable or iterator, going left to right.
Note: /: is alternate syntax for foldLeft; z /: xs is the same as xs foldLeft z.
Examples:
Note that the folding function used to compute b is equivalent to that used to compute c.
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = (5 /: a)(_+_) b: Int = 15 scala> val c = (5 /: a)((x,y) => x + y) c: Int = 15
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.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this traversable or iterator, going left to right with the start value z on the left:
op(...op(op(z, x_1), x_2), ..., x_n)
where x1, ..., xn are the elements of this traversable or iterator.
A copy of this stream with an element appended.
A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.
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)
the appended element
a new stream consisting of all elements of this stream followed by elem.
Applies a binary operator to all elements of this traversable or iterator and a start value, going right to left.
Note: :\ is alternate syntax for foldRight; xs :\ z is the same as xs foldRight z.
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.
Examples:
Note that the folding function used to compute b is equivalent to that used to compute c.
scala> val a = List(1,2,3,4) a: List[Int] = List(1, 2, 3, 4) scala> val b = (a :\ 5)(_+_) b: Int = 15 scala> val c = (a :\ 5)((x,y) => x + y) c: Int = 15
the result type of the binary operator.
the start value
the binary operator
the result of inserting op between consecutive elements of this traversable or iterator, 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 traversable or iterator.
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
true if the receiver object is equivalent to the argument; false otherwise.
Write all defined elements of this iterable into given string builder. The written text begins with the string start and is finished by the string end. Inside, the string representations of defined elements (w.r.t. the method toString()) are separated by the string sep. The method will not force evaluation of undefined elements. A tail of such elements will be represented by a "?" instead. A cyclic stream is represented by a "..." at the point where the cycle repeats.
The collection.mutable.StringBuilder factory to which we need to add the string elements.
The prefix of the resulting string (e.g. "Stream(")
The separator between elements of the resulting string (e.g. ",")
The end of the resulting string (e.g. ")")
The original collection.mutable.StringBuilder containing the resulting string.
Appends all elements of this traversable or iterator to a string builder. The written text consists of the string representations (w.r.t. the method toString) of all elements of this traversable or iterator 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
the string builder to which elements are appended.
the string builder b to which elements were appended.
Appends all elements of this traversable or iterator 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 traversable or iterator, 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
the string builder to which elements are appended.
the separator string.
the string builder b to which elements were appended.
Aggregates the results of applying an operator to subsequent elements.
This is a more general form of fold and reduce. It is similar to foldLeft in that it doesn't require the result to be a supertype of the element type. In addition, it allows parallel collections to be processed in chunks, and then combines the intermediate results.
aggregate splits the traversable or iterator into partitions and processes each partition by sequentially applying seqop, starting with z (like foldLeft). Those intermediate results are then combined by using combop (like fold). The implementation of this operation may operate on an arbitrary number of collection partitions (even 1), so combop may be invoked an arbitrary number of times (even 0).
As an example, consider summing up the integer values of a list of chars. The initial value for the sum is 0. First, seqop transforms each input character to an Int and adds it to the sum (of the partition). Then, combop just needs to sum up the intermediate results of the partitions:
List('a', 'b', 'c').aggregate(0)({ (sum, ch) => sum + ch.toInt }, { (p1, p2) => p1 + p2 })
the type of accumulated results
the initial value for the accumulated result of the partition - this will typically be the neutral element for the seqop operator (e.g. Nil for list concatenation or 0 for summation) and may be evaluated more than once
an operator used to accumulate results within a partition
an associative operator used to combine results from different partitions
Composes this partial function with a transformation function that gets applied to results of this partial function.
the result type of the transformation function.
the transformation function
a partial function with the same domain as this partial function, which maps arguments x to k(this(x)).
The stream resulting from the concatenation of this stream with the argument stream.
The stream that gets appended to this stream
The stream containing elements of this stream and the traversable object.
Selects an element by its index in the sequence. Note: the execution of apply may take time proportional to the index value.
the element of this sequence at index idx, where 0 indicates the first element.
IndexOutOfBoundsException if idx does not satisfy 0 <= idx < length.
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:
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.
the function argument
the fallback function
the result of this function or fallback function application.
2.10
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.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Method called from equality methods, so that user-defined subclasses can refuse to be equal to other collections of the same kind.
The object with which this iterable collection should be compared
true, if this iterable collection can possibly equal that, false otherwise. The test takes into consideration only the run-time types of objects but ignores their elements.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
Builds a new collection by applying a partial function to all elements of this stream on which the function is defined.
the element type of the returned collection.
the partial function which filters and maps the stream.
a new stream 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.
Finds the first element of the traversable or iterator 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.
the partial function
an option value containing pf applied to the first value for which it is defined, or None if none exists.
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
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.
An Iterator which traverses the possible n-element combinations of this sequence.
"abbbc".combinations(2) = Iterator(ab, ac, bb, bc)
The factory companion object that builds instances of class Stream. (or its Iterable superclass where class Stream is not a Seq.)
Composes two instances of Function1 in a new Function1, with this function applied last.
the type to which function g can be applied
a function A => T1
a new function f such that f(x) == apply(g(x))
Tests whether this sequence contains a given value as an element.
Note: may not terminate for infinite-sized collections.
the element to test.
true if this sequence has an element that is equal (as determined by ==) to elem, false otherwise.
Tests whether this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
true if this sequence contains a slice with the same elements as that, otherwise false.
Copies the elements of this stream to an array. Fills the given array xs with at most len elements of this stream, starting at position start. Copying will stop once either the end of the current stream is reached, or the end of the target array is reached, or len elements have been copied.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
the maximal number of elements to copy.
Copies the elements of this stream to an array. Fills the given array xs with values of this stream. Copying will stop once either the end of the current stream is reached, or the end of the target array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
Copies the elements of this stream to an array. Fills the given array xs with values of this stream, beginning at index start. Copying will stop once either the end of the current stream is reached, or the end of the target array is reached.
Note: will not terminate for infinite-sized collections.
the array to fill.
the starting index.
Copies all elements of this traversable or iterator to a buffer.
Note: will not terminate for infinite-sized collections.
The buffer to which elements are copied.
Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.
the type of the elements of that
the other sequence
the test predicate, which relates elements from both sequences
true if both sequences have the same length and p(x, y) is true for all corresponding elements x of this sequence and y of that, otherwise false.
Counts the number of elements in the traversable or iterator which satisfy a predicate.
the predicate used to test elements.
the number of elements satisfying the predicate p.
Computes the multiset difference between this stream and another sequence.
Note: will not terminate for infinite-sized collections.
the sequence of elements to remove
a new stream which contains all elements of this stream 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.
Builds a new stream from this stream in which any duplicates (as determined by ==) have been removed. Among duplicate elements, only the first one is retained in the resulting Stream.
A new Stream representing the result of applying distinctness to the original Stream.
// Creates a Stream where every element is duplicated
def naturalsFrom(i: Int): Stream[Int] = i #:: { i #:: naturalsFrom(i + 1) }
naturalsFrom(1) take 6 mkString ", "
// produces: "1, 1, 2, 2, 3, 3"
(naturalsFrom(1) distinct) take 6 mkString ", "
// produces: "1, 2, 3, 4, 5, 6"
Selects all elements except first n ones.
the number of elements to drop from this stream.
a stream consisting of all elements of this stream except the first n ones, or else the empty stream, if this stream has less than n elements. If n is negative, don't drop any elements.
Selects all elements except last n ones.
Note: lazily evaluated; will terminate for infinite-sized collections.
The number of elements to take
a stream consisting of all elements of this stream except the last n ones, or else the empty stream, if this stream has less than n elements.
Returns the a Stream representing the longest suffix of this iterable whose first element does not satisfy the predicate p.
the test predicate.
A new Stream representing the results of applying p to the original Stream.
// Assume we have a Stream that takes the first 20 natural numbers
def naturalsLt50(i: Int): Stream[Int] = i #:: { if (i < 20) naturalsLt50(i * + 1) else Stream.Empty }
naturalsLt50(0) dropWhile { _ < 10 }
// produces: "10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20"
This method realizes the entire Stream beyond the truth value of the predicate p.
Tests whether this sequence ends with the given sequence.
Note: will not terminate for infinite-sized collections.
the sequence to test
true if this sequence has that as a suffix, false otherwise.
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:
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).
true if the argument is a reference to the receiver object; false otherwise.
The equals method for arbitrary sequences. Compares this sequence to some other object.
The object to compare the sequence to
true if that is a sequence that has the same elements as this sequence in the same order, false otherwise
Tests whether a predicate holds for at least one element of this sequence.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
false if this sequence is empty, otherwise true if the given predicate p holds for some of the elements of this sequence, otherwise false
Selects all elements of this traversable collection which satisfy a predicate.
the predicate used to test elements.
a new traversable collection consisting of all elements of this traversable collection that satisfy the given predicate p. The order of the elements is preserved.
Selects all elements of this traversable collection which do not satisfy a predicate.
the predicate used to test elements.
a new traversable collection consisting of all elements of this traversable collection that do not satisfy the given predicate p. The order of the elements is preserved.
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.
not specified by SLS as a member of AnyRef
Finds the first element of the sequence satisfying a predicate, if any.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
an option value containing the first element in the sequence that satisfies p, or None if none exists.
Applies the given function f to each element of this stream, then concatenates the results. As with map this function does not need to realize the entire Stream but continues to keep it as a lazy Stream.
The element type of the returned collection That.
the class of the returned collection. Where possible, That is the same class as the current collection class Repr, but this depends on the element type B being admissible for that class, which means that an implicit instance of type CanBuildFrom[Repr, B, That] is found.
the function to apply on each element.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
f(a0) ::: ... ::: f(an) if this stream is [a0, ..., an].
// Let's create a Stream of Vectors, each of which contains the
// collection of Fibonacci numbers up to the current value. We
// can then 'flatMap' that Stream.
val fibVec: Stream[Vector[Int]] = Vector(0) #:: Vector(0, 1) #:: fibVec.zip(fibVec.tail).map(n => {
n._2 ++ Vector(n._1.last + n._2.last)
})
fibVec take 5 foreach println
// prints
// Vector(0)
// Vector(0, 1)
// Vector(0, 1, 1)
// Vector(0, 1, 1, 2)
// Vector(0, 1, 1, 2, 3)
// If we now want to `flatMap` across that stream by adding 10
// we can see what the series turns into:
fibVec.flatMap(_.map(_ + 10)) take 15 mkString(", ")
// produces: 10, 10, 11, 10, 11, 11, 10, 11, 11, 12, 10, 11, 11, 12, 13
Note: Currently flatMap will evaluate as much of the Stream as needed until it finds a non-empty element for the head, which is non-lazy.
Evaluates and concatenates all elements within the Stream into a new flattened Stream.
The type of the elements of the resulting Stream.
an implicit conversion which asserts that the element type of this stream is a GenTraversable.
A new Stream of type B of the flattened elements of this Stream.
val sov: Stream[Vector[Int]] = Vector(0) #:: Vector(0, 0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }
sov.flatten take 10 mkString ", "
// produces: "0, 0, 0, 0, 0, 0, 0, 0, 0, 0"
Folds the elements of this traversable or iterator using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
Note: will not terminate for infinite-sized collections.
a type parameter for the binary operator, a supertype of A.
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).
a binary operator that must be associative.
the result of applying the fold operator op between all the elements and z, or z if this traversable or iterator is empty.
Stream specialization of foldLeft which allows GC to collect along the way.
The type of value being accumulated.
The initial value seeded into the function op.
The operation to perform on successive elements of the Stream.
The accumulated value from successive applications of op.
Applies a binary operator to all elements of this sequence and a start value, going right to left.
Note: will not terminate for infinite-sized collections.
the result type of the binary operator.
the start value.
the binary operator.
the result of inserting op between consecutive elements of this sequence, 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 sequence. Returns z if this sequence is empty.
Tests whether a predicate holds for all elements of this sequence.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
true if this sequence is empty or the given predicate p holds for all elements of this sequence, otherwise false.
Forces evaluation of the whole stream and returns it.
The fully realized Stream.
Often we use Streams to represent an infinite set or series. If that's the case for your particular Stream then this function will never return and will probably crash the VM with an OutOfMemory exception. This function will not hang on a finite cycle, however.
Apply the given function f to each element of this linear sequence (while respecting the order of the elements).
the type parameter describing the result of function f. This result will always be ignored. Typically U is Unit, but this is not necessary.
The treatment to apply to each element.
Overridden here as final to trigger tail-call optimization, which replaces 'this' with 'tail' at each iteration. This is absolutely necessary for allowing the GC to collect the underlying stream as elements are consumed.
,This function will force the realization of the entire stream unless the f throws an exception.
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).
The generic builder that builds instances of Traversable at arbitrary element types.
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
Partitions this traversable collection into a map of traversable collections according to some discriminator function.
Note: this method is not re-implemented by views. This means when applied to a view it will always force the view and return a new traversable collection.
the type of keys returned by the discriminator function.
the discriminator function.
A map from keys to traversable 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 traversable collection of those elements x for which f(x) equals k.
Partitions elements in fixed size iterable collections.
the number of elements per group
An iterator producing iterable collections of size size, except the last will be less than size size if the elements don't divide evenly.
scala.collection.Iterator, method grouped
Tests whether this stream is known to have a finite size. All strict collections are known to have finite size. For a non-strict collection such as Stream, the predicate returns true if all elements have been computed. It returns false if the stream is not yet evaluated to the end. Non-empty Iterators usually return false even if they were created from a collection with a known finite size.
Note: many collection methods will not work on collections of infinite sizes. The typical failure mode is an infinite loop. These methods always attempt a traversal without checking first that hasDefiniteSize returns true. However, checking hasDefiniteSize can provide an assurance that size is well-defined and non-termination is not a concern.
true if this collection is known to have finite size, false otherwise.
Hashcodes for Seq produce a value from the hashcodes of all the elements of the sequence.
the hash code value for this object.
Selects the first element of this iterable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this iterable collection.
NoSuchElementException if the iterable collection is empty.
Optionally selects the first element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the first element of this traversable collection if it is nonempty, None if it is empty.
Finds index of first occurrence of some value in this stream after or at some start index.
Note: may not terminate for infinite-sized collections.
the element value to search for.
the start index
the index >= from of the first element of this stream that is equal (as determined by ==) to elem, or -1, if none exists.
Finds index of first occurrence of some value in this stream.
Note: may not terminate for infinite-sized collections.
the element value to search for.
the index of the first element of this stream that is equal (as determined by ==) to elem, or -1, if none exists.
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.
the sequence to test
the start index
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.
Finds first index where this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
the sequence to test
the first 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.
Finds index of the first element satisfying some predicate after or at some start index.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the start index
the index >= from of the first element of this sequence that satisfies the predicate p, or -1, if none exists.
Finds index of first element satisfying some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the index of the first element of this general sequence that satisfies the predicate p, or -1, if none exists.
Produces the range of all indices of this sequence.
a Range value from 0 to one less than the length of this sequence.
The stream without its last element.
A new Stream containing everything but the last element. If your Stream represents an infinite series, this method will not return.
UnsupportedOperationException if the stream is empty.
Iterates over the inits of this traversable collection. The first value will be this traversable collection and the final one will be an empty traversable collection, with the intervening values the results of successive applications of init.
an iterator over all the inits of this traversable collection
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)
Computes the multiset intersection between this stream and another sequence.
Note: may not terminate for infinite-sized collections.
the sequence of elements to intersect with.
a new stream which contains all elements of this stream 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.
Tests whether this sequence contains given index.
The implementations of methods apply and isDefinedAt turn a Seq[A] into a PartialFunction[Int, A].
true if this sequence contains an element at position idx, false otherwise.
Tests whether this sequence is empty.
true if the sequence contain no elements, false otherwise.
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.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Tests whether this traversable collection can be repeatedly traversed.
true
A lazier Iterator than LinearSeqLike's.
the new iterator
Selects the last element.
The last element of this sequence.
NoSuchElementException If the sequence is empty.
Finds index of last occurrence of some value in this stream before or at a given end index.
the element value to search for.
the end index.
the index <= end of the last element of this stream that is equal (as determined by ==) to elem, or -1, if none exists.
Finds index of last occurrence of some value in this stream.
Note: will not terminate for infinite-sized collections.
the element value to search for.
the index of the last element of this stream that is equal (as determined by ==) to elem, or -1, if none exists.
Finds last index before or at a given end index where this sequence contains a given sequence as a slice.
the sequence to test
the end index
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.
Finds last index where this sequence contains a given sequence as a slice.
Note: will not terminate for infinite-sized collections.
the sequence to test
the last index such that the elements of this sequence starting a this index match the elements of sequence that, or -1 of no such subsequence exists.
Finds index of last element satisfying some predicate before or at given end index.
the predicate used to test elements.
the index <= end of the last element of this sequence that satisfies the predicate p, or -1, if none exists.
Finds index of last element satisfying some predicate.
Note: will not terminate for infinite-sized collections.
the predicate used to test elements.
the index of the last element of this general sequence that satisfies the predicate p, or -1, if none exists.
Optionally selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
the last element of this traversable collection$ if it is nonempty, None if it is empty.
Returns the length of this Stream.
The length of this Stream.
In order to compute the length of the Stream, it must first be fully realized, which could cause the complete evaluation of an infinite series, assuming that's what your Stream represents.
Compares the length of this sequence to a test value.
the test value that gets compared with the length.
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 overwritten if computing length is cheap.
Turns this partial function into a plain function returning an Option result.
a function that takes an argument x to Some(this(x)) if this is defined for x, and to None otherwise.
Function.unlift
Returns the stream resulting from applying the given function f to each element of this stream. This returns a lazy Stream such that it does not need to be fully realized.
The element type of the returned collection That.
the class of the returned collection. Where possible, That is the same class as the current collection class Repr, but this depends on the element type B being admissible for that class, which means that an implicit instance of type CanBuildFrom[Repr, B, That] is found.
function to apply to each element.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
f(a0), ..., f(an) if this sequence is a0, ..., an.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
naturalsFrom(1).map(_ + 10) take 5 mkString(", ")
// produces: "11, 12, 13, 14, 15"
Finds the largest element.
the largest element of this stream.
UnsupportedOperationException if this stream is empty.
Finds the first element which yields the largest value measured by function f.
The result type of the function f.
The measuring function.
the first element of this stream with the largest value measured by function f.
UnsupportedOperationException if this stream is empty.
Finds the smallest element.
the smallest element of this stream
UnsupportedOperationException if this stream is empty.
Finds the first element which yields the smallest value measured by function f.
The result type of the function f.
The measuring function.
the first element of this stream with the smallest value measured by function f.
UnsupportedOperationException if this stream is empty.
Displays all elements of this stream in a string using start, end, and separator strings.
the starting string.
the separator string.
the ending string.
a string representation of this stream. 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 stream are separated by the string sep.
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
Displays all elements of this stream in a string.
a string representation of this stream. In the resulting string the string representations (w.r.t. the method toString) of all elements of this stream follow each other without any separator string.
Displays all elements of this stream in a string using a separator string.
the separator string.
a string representation of this stream. In the resulting string the string representations (w.r.t. the method toString) of all elements of this stream are separated by the string sep.
List(1, 2, 3).mkString("|") = "1|2|3"
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
The builder that builds instances of type Traversable[A]
Tests whether the traversable or iterator is not empty.
true if the traversable or iterator contains at least one element, false otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
the argument type of the fallback function
the result type of the fallback function
the fallback function
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.
Returns a new sequence of given length containing the elements of this sequence followed by zero or more occurrences of given elements.
The type of the value to pad with.
The type contained within the resulting Stream.
The number of elements to pad into the Stream.
The value of the type B to use for padding.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
A new Stream representing the collection with values padding off to the end. If your Stream represents an infinite series, this method will not return.
def naturalsFrom(i: Int): Stream[Int] = i #:: { if (i < 5) naturalsFrom(i + 1) else Stream.Empty }
naturalsFrom(1) padTo(10, 0) foreach println
// prints
// 1
// 2
// 3
// 4
// 5
// 0
// 0
// 0
// 0
// 0
Returns a parallel implementation of this collection.
For most collection types, this method creates a new parallel collection by copying all the elements. For these collection, par takes linear time. Mutable collections in this category do not produce a mutable parallel collection that has the same underlying dataset, so changes in one collection will not be reflected in the other one.
Specific collections (e.g. ParArray or mutable.ParHashMap) override this default behaviour by creating a parallel collection which shares the same underlying dataset. For these collections, par takes constant or sublinear time.
All parallel collections return a reference to themselves.
a parallel implementation of this collection
The default par implementation uses the combiner provided by this method to create a new parallel collection.
a combiner for the parallel collection of type ParRepr
Returns all the elements of this stream that satisfy the predicate p returning of scala.Tuple2 of Streams obeying the partition predicate p. The order of the elements is preserved.
the predicate used to filter the stream.
the elements of this stream satisfying p.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1)
val parts = naturalsFrom(1) partition { _ % 2 == 0 }
parts._1 take 10 mkString ", "
// produces: "2, 4, 6, 8, 10, 12, 14, 16, 18, 20"
parts._2 take 10 mkString ", "
// produces: "1, 3, 5, 7, 9, 11, 13, 15, 17, 19"
Produces a new stream where a slice of elements in this stream is replaced by another sequence.
the index of the first replaced element
the number of elements to drop in the original stream
a new stream consisting of all elements of this stream except that replaced elements starting from from are replaced by patch.
Iterates over distinct permutations.
An Iterator which traverses the distinct permutations of this sequence.
"abb".permutations = Iterator(abb, bab, bba)
Returns the length of the longest prefix whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the length of the longest prefix of this general sequence such that every element of the segment satisfies the predicate p.
Prints elements of this stream one by one, separated by sep.
The separator string printed between consecutive elements.
Multiplies up the elements of this collection.
the product of all elements in this stream of numbers of type Int. Instead of Int, any other type T with an implicit Numeric[T] implementation can be used as element type of the stream and as result type of product. Examples of such types are: Long, Float, Double, BigInt.
Reduces the elements of this traversable or iterator using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
A type parameter for the binary operator, a supertype of A.
A binary operator that must be associative.
The result of applying reduce operator op between all the elements if the traversable or iterator is nonempty.
UnsupportedOperationException if this traversable or iterator is empty.
Stream specialization of reduceLeft which allows GC to collect along the way.
The type of value being accumulated.
The operation to perform on successive elements of the Stream.
The accumulated value from successive applications of f.
Optionally applies a binary operator to all elements of this traversable or iterator, 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.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceLeft(op) if this traversable or iterator is nonempty, None otherwise.
Reduces the elements of this traversable or iterator, if any, using the specified associative binary operator.
The order in which operations are performed on elements is unspecified and may be nondeterministic.
A type parameter for the binary operator, a supertype of A.
A binary operator that must be associative.
An option value containing result of applying reduce operator op between all the elements if the collection is nonempty, and None otherwise.
Applies a binary operator to all elements of this sequence, going right to left.
Note: will not terminate for infinite-sized collections.
the result type of the binary operator.
the binary operator.
the result of inserting op between consecutive elements of this sequence, going right to left:
op(x_1, op(x_2, ..., op(x_{n-1}, x_n)...))
where x1, ..., xn are the elements of this sequence.
UnsupportedOperationException if this sequence is empty.
Optionally applies a binary operator to all elements of this traversable or iterator, 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.
the result type of the binary operator.
the binary operator.
an option value containing the result of reduceRight(op) if this traversable or iterator is nonempty, None otherwise.
The collection of type traversable collection underlying this TraversableLike object. By default this is implemented as the TraversableLike object itself, but this can be overridden.
A list consisting of all elements of this list in reverse order.
A new Stream containing the representing of the original Stream in reverse order.
def naturalsFrom(i: Int): Stream[Int] = i #:: { if (i < 5) naturalsFrom(i + 1) else Stream.Empty }
(naturalsFrom(1) reverse) foreach println
// prints
// 5
// 4
// 3
// 2
// 1
This function must realize the entire Stream in order to perform this operation so if your Stream represents an infinite sequence then this function will never return.
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.
an iterator yielding the elements of this sequence in reversed order
Builds a new collection by applying a function to all elements of this stream and collecting the results in reversed order.
Note: will not terminate for infinite-sized collections.
Note: xs.reverseMap(f) is the same as xs.reverse.map(f) but might be more efficient.
the element type of the returned collection.
the function to apply to each element.
a new stream resulting from applying the given function f to each element of this stream and collecting the results in reversed order.
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.
the action function
a function which maps arguments x to isDefinedAt(x). The resulting function runs action(this(x)) where this is defined.
2.10
applyOrElse.
Checks if the other iterable collection contains the same elements in the same order as this stream.
Note: will not terminate for infinite-sized collections.
the collection to compare with.
true, if both collections contain the same elements in the same order, false otherwise.
Computes a prefix scan of the elements of the collection.
Note: The neutral element z may be applied more than once.
element type of the resulting collection
type of the resulting collection
neutral element for the operator op
the associative operator for the scan
combiner factory which provides a combiner
a new traversable collection containing the prefix scan of the elements in this traversable collection
Create a new stream which contains all intermediate results of applying the operator to subsequent elements left to right. scanLeft is analogous to foldLeft.
the type of the elements in the resulting collection
the actual type of the resulting collection
The initial value for the scan.
A function that will apply operations to successive values in the Stream against previous accumulated results.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
A new collection containing the modifications from the application of op.
This works because the target type of the scala.collection.mutable.Builder That is a Stream.
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.
Example:
List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
the type of the elements in the resulting collection
the actual type of the resulting collection
the initial value
the binary operator applied to the intermediate result and the element
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type B.
collection with intermediate results
(Changed in version 2.9.0) The behavior of scanRight has changed. The previous behavior can be reproduced with scanRight.reverse.
Computes length of longest segment whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
the predicate used to test elements.
the index where the search starts.
the length of the longest segment of this sequence starting from index from such that every element of the segment satisfies the predicate p.
A version of this collection with all of the operations implemented sequentially (i.e., in a single-threaded manner).
This method returns a reference to this collection. In parallel collections, it is redefined to return a sequential implementation of this collection. In both cases, it has O(1) complexity.
a sequential view of the collection.
The size of this sequence, equivalent to length.
Note: will not terminate for infinite-sized collections.
the number of elements in this sequence.
The size of this collection or iterator, if it can be cheaply computed
the number of elements in this collection or iterator, or -1 if the size cannot be determined cheaply
A substream starting at index from and extending up to (but not including) index until. This returns a Stream that is lazily evaluated.
The index of the first element of the returned subsequence
The index of the element following the returned subsequence
A new string containing the elements requested from start until end.
naturalsFrom(0) slice(50, 60) mkString ", " // produces: "50, 51, 52, 53, 54, 55, 56, 57, 58, 59"
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
the number of elements per group
the distance between the first elements of successive groups
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.
scala.collection.Iterator, method sliding
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.
the number of elements per group
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.
scala.collection.Iterator, method sliding
Sorts this Seq according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.
the target type of the transformation f, and the type where the ordering ord is defined.
the transformation function mapping elements to some other domain B.
the ordering assumed on domain B.
a sequence consisting of the elements of this sequence sorted according to the ordering where x < y if ord.lt(f(x), f(y)).
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)
scala.math.Ordering Note: will not terminate for infinite-sized collections.
Sorts this sequence according to a comparison function.
Note: will not terminate for infinite-sized collections.
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.
the comparison function which tests whether its first argument precedes its second argument in the desired ordering.
a sequence consisting of the elements of this sequence sorted according to the comparison function lt.
List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) =
List("Bob", "John", "Steve", "Tom")
Sorts this sequence according to an Ordering.
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.
the ordering to be used to compare elements.
a sequence consisting of the elements of this sequence sorted according to the ordering ord.
Splits this sequence 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.
a pair consisting of the longest prefix of this sequence whose elements all satisfy p, and the rest of this sequence.
Splits this stream into two at a given position. Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n).
the position at which to split.
a pair of streams consisting of the first n elements of this stream, and the other elements.
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.
the sequence to test
the index where the sequence is searched.
true if the sequence that is contained in this sequence at index offset, otherwise false.
Tests whether this general sequence starts with the given sequence.
the sequence to test
true if this collection has that as a prefix, false otherwise.
Defines the prefix of this object's toString representation as Stream.
a string representation which starts the result of toString applied to this stream. By default the string prefix is the simple name of the collection class stream.
Sums up the elements of this collection.
the sum of all elements in this stream of numbers of type Int. Instead of Int, any other type T with an implicit Numeric[T] implementation can be used as element type of the stream and as result type of sum. Examples of such types are: Long, Float, Double, BigInt.
Selects all elements except the first.
Note: might return different results for different runs, unless the underlying collection type is ordered.
a traversable collection consisting of all elements of this traversable collection except the first one.
java.lang.UnsupportedOperationException if the traversable collection is empty.
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.
an iterator over all the tails of this sequence
List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)
Returns the n first elements of this Stream as another Stream, or else the whole Stream, if it has less than n elements.
The result of take is, again, a Stream meaning that it also does not make any needless evaluations of the Stream itself, delaying that until the usage of the resulting Stream.
the number of elements to take.
the n first elements of this stream.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) scala> naturalsFrom(5) take 5 res1: scala.collection.immutable.Stream[Int] = Stream(5, ?) scala> naturalsFrom(5) take 5 mkString ", " // produces: "5, 6, 7, 8, 9"
Returns the rightmost n elements from this iterable.
the number of elements to take
The last n elements from this Stream.
Take serious caution here. If the Stream represents an infinite series then this function will not return. The right most elements of an infinite series takes an infinite amount of time to produce.
Returns the longest prefix of this Stream whose elements satisfy the predicate p.
the test predicate.
A new Stream representing the values that satisfy the predicate p.
+ naturalsFrom(0) takeWhile { _ < 5 } mkString ", "
produces: "0, 1, 2, 3, 4"
The underlying collection seen as an instance of Seq
Converts this stream into another by copying all elements.
Note: will not terminate for infinite-sized collections.
The collection type to build.
a new collection containing all elements of this stream.
Converts this stream to an array.
Note: will not terminate for infinite-sized collections.
an array containing all elements of this stream. An ClassTag must be available for the element type of this stream.
Uses the contents of this traversable or iterator to create a new mutable buffer.
Note: will not terminate for infinite-sized collections.
a buffer containing all elements of this traversable or iterator.
A conversion from collections of type Repr to Seq
Converts this traversable or iterator to an indexed sequence.
Note: will not terminate for infinite-sized collections.
an indexed sequence containing all elements of this traversable or iterator.
Returns this iterable collection as an iterable collection.
A new collection will not be built; lazy collections will stay lazy.
Note: will not terminate for infinite-sized collections.
an Iterable containing all elements of this iterable collection.
Returns an Iterator over the elements in this iterable collection. Produces the same result as iterator.
Note: will not terminate for infinite-sized collections.
an Iterator containing all elements of this iterable collection.
Converts this traversable or iterator to a list.
Note: will not terminate for infinite-sized collections.
a list containing all elements of this traversable or iterator.
Converts this stream to a map. This method is unavailable unless the elements are members of Tuple2, each ((T, U)) becoming a key-value pair in the map. Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key is in the resulting map is undefined.
Note: will not terminate for infinite-sized collections.
a map of type immutable.Map[T, U] containing all key/value pairs of type (T, U) of this stream.
Converts this immutable sequence to a sequence.
Note: will not terminate for infinite-sized collections.
A new collection will not be built; in particular, lazy sequences will stay lazy.
a sequence containing all elements of this immutable sequence.
Converts this traversable or iterator to a set.
Note: will not terminate for infinite-sized collections.
a set containing all elements of this traversable or iterator.
Converts this stream to a stream.
a stream containing all elements of this stream.
Converts this stream to a string.
a string representation of this collection. By default this string consists of the stringPrefix of this stream, followed by all elements separated by commas and enclosed in parentheses.
Converts this traversable collection to an unspecified Traversable. Will return the same collection if this instance is already Traversable.
Note: will not terminate for infinite-sized collections.
a Traversable containing all elements of this traversable collection.
Converts this traversable or iterator to a Vector.
Note: will not terminate for infinite-sized collections.
a vector containing all elements of this traversable or iterator.
Transposes this collection of traversable collections into a collection of collections.
The resulting collection's type will be guided by the static type of 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))
the type of the elements of each traversable collection.
an implicit conversion which asserts that the element type of this collection is a Traversable.
a two-dimensional collection of collections which has as nth row the nth column of this collection.
(Changed in version 2.9.0) transpose throws an IllegalArgumentException if collections are not uniformly sized.
IllegalArgumentException if all collections in this collection are not of the same size.
Produces a new sequence which contains all elements of this stream and also all elements of a given sequence. xs union ys is equivalent to xs ++ ys.
Another way to express this is that xs union ys computes the order-preserving multi-set union of xs and ys. union is hence a counter-part of diff and intersect which also work on multi-sets.
Note: will not terminate for infinite-sized collections.
the sequence to add.
a new stream which contains all elements of this stream followed by all elements of that.
Converts this collection of pairs into two collections of the first and second half of each pair.
val xs = Traversable(
(1, "one"),
(2, "two"),
(3, "three")).unzip
// xs == (Traversable(1, 2, 3),
// Traversable(one, two, three))
the type of the first half of the element pairs
the type of the second half of the element pairs
an implicit conversion which asserts that the element type of this collection is a pair.
a pair of collections, containing the first, respectively second half of each element pair of this collection.
Converts this collection of triples into three collections of the first, second, and third element of each triple.
val xs = Traversable(
(1, "one", '1'),
(2, "two", '2'),
(3, "three", '3')).unzip3
// xs == (Traversable(1, 2, 3),
// Traversable(one, two, three),
// Traversable(1, 2, 3))
the type of the first member of the element triples
the type of the second member of the element triples
the type of the third member of the element triples
an implicit conversion which asserts that the element type of this collection is a triple.
a triple of collections, containing the first, second, respectively third member of each element triple of this collection.
A copy of this stream with one single replaced element.
the position of the replacement
the replacing element
a copy of this stream with the element at position index replaced by elem.
Creates a non-strict view of this stream.
a non-strict view of this stream.
Creates a non-strict view of a slice of this sequence.
Note: the difference between view and slice is that view produces a view of the current sequence, whereas slice produces a new sequence.
Note: view(from, to) is equivalent to view.slice(from, to)
the index of the first element of the view
the index of the element following the view
a non-strict view of a slice of this sequence, starting at index from and extending up to (but not including) index until.
A FilterMonadic which allows GC of the head of stream during processing
the predicate used to test elements.
an object of class WithFilter, which supports map, flatMap, foreach, and withFilter operations. All these operations apply to those elements of this stream which satisfy the predicate p.
Returns a stream formed from this stream and the specified stream that by associating each element of the former with the element at the same position in the latter.
If one of the two streams is longer than the other, its remaining elements are ignored.
The return type of this function may not be obvious. The lazy aspect of the returned value is different than that of partition. In partition we get back a scala.Tuple2 of two lazy Streams whereas here we get back a single lazy Stream of scala.Tuple2s where the scala.Tuple2's type signature is (A1, B).
The type of the first parameter of the zipped tuple
The type of the second parameter of the zipped tuple
The type of the returned Stream.
The iterable providing the second half of each result pair
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type (A1, B).
Stream({a0,b0}, ...,
{amin(m,n),bmin(m,n))} when Stream(a0, ..., am)
zip Stream(b0, ..., bn) is invoked.
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) naturalsFrom(1) zip naturalsFrom(2) take 5 foreach println // prints // (1,2) // (2,3) // (3,4) // (4,5) // (5,6)
Returns a stream formed from this stream 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.
the type of the second half of the returned pairs
The iterable providing the second half of each result pair
the element to be used to fill up the result if this stream is shorter than that.
the element to be used to fill up the result if that is shorter than this stream.
a new stream containing pairs consisting of corresponding elements of this stream and that. The length of the returned collection is the maximum of the lengths of this stream and that. If this stream is shorter than that, thisElem values are used to pad the result. If that is shorter than this stream, thatElem values are used to pad the result.
Zips this iterable with its indices. s.zipWithIndex is equivalent to s
zip s.indices.
This method is much like zip in that it returns a single lazy Stream of scala.Tuple2.
The type of the first element of the scala.Tuple2 in the resulting stream.
The type of the resulting Stream.
an implicit value of class CanBuildFrom which determines the result class That from the current representation type Repr and the new element type (A1, Int).
Stream({a0,0}, ..., {an,n)}
def naturalsFrom(i: Int): Stream[Int] = i #:: naturalsFrom(i + 1) (naturalsFrom(1) zipWithIndex) take 5 foreach println // prints // (1,0) // (2,1) // (3,2) // (4,3) // (5,4)
(stream: MonadOps[A]).filter(p)
(stream: MonadOps[A]).flatMap(f)
(stream: MonadOps[A]).map(f)
(stream: MonadOps[A]).withFilter(p)
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala/collection/immutable/Stream.html
The class
Streamimplements lazy lists where elements are only evaluated when they are needed. Here is an example:import scala.math.BigInt object Main extends App { lazy val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map { n => n._1 + n._2 } fibs take 5 foreach println } // prints // // 0 // 1 // 1 // 2 // 3The
Streamclass also employs memoization such that previously computed values are converted fromStreamelements to concrete values of typeA. To illustrate, we will alter body of thefibsvalue above and take some more values:import scala.math.BigInt object Main extends App { lazy val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip( fibs.tail).map(n => { println("Adding %d and %d".format(n._1, n._2)) n._1 + n._2 }) fibs take 5 foreach println fibs take 6 foreach println } // prints // // 0 // 1 // Adding 0 and 1 // 1 // Adding 1 and 1 // 2 // Adding 1 and 2 // 3 // And then prints // // 0 // 1 // 1 // 2 // 3 // Adding 2 and 3 // 5There are a number of subtle points to the above example.
fibsis avalnot a method. The memoization of theStreamrequires us to have somewhere to store the information and avalallows us to do that.Streamis actually being modified during access, this does not change the notion of its immutability. Once the values are memoized they do not change and values that have yet to be memoized still "exist", they simply haven't been realized yet.Streamcreates a structure much like scala.collection.immutable.List. So long as something is holding on to the head, the head holds on to the tail, and so it continues recursively. If, on the other hand, there is nothing holding on to the head (e.g. we useddefto define theStream) then once it is no longer being used directly, it disappears.Stream, and a stream holds its own head. For computations of this sort where memoization is not desired, useIteratorwhen possible.// For example, let's build the natural numbers and do some silly iteration // over them. // We'll start with a silly iteration def loop(s: String, i: Int, iter: Iterator[Int]): Unit = { // Stop after 200,000 if (i < 200001) { if (i % 50000 == 0) println(s + i) loop(s, iter.next, iter) } } // Our first Stream definition will be a val definition val stream1: Stream[Int] = { def loop(v: Int): Stream[Int] = v #:: loop(v + 1) loop(0) } // Because stream1 is a val, everything that the iterator produces is held // by virtue of the fact that the head of the Stream is held in stream1 val it1 = stream1.iterator loop("Iterator1: ", it1.next, it1) // We can redefine this Stream such that all we have is the Iterator left // and allow the Stream to be garbage collected as required. Using a def // to provide the Stream ensures that no val is holding onto the head as // is the case with stream1 def stream2: Stream[Int] = { def loop(v: Int): Stream[Int] = v #:: loop(v + 1) loop(0) } val it2 = stream2.iterator loop("Iterator2: ", it2.next, it2) // And, of course, we don't actually need a Stream at all for such a simple // problem. There's no reason to use a Stream if you don't actually need // one. val it3 = new Iterator[Int] { var i = -1 def hasNext = true def next(): Int = { i += 1; i } } loop("Iterator3: ", it3.next, it3)tailworks at all is of interest. In the definition offibswe have an initial(0, 1, Stream(...))sotailis deterministic. If we definedfibssuch that only0were concretely known then the act of determiningtailwould require the evaluation oftailwhich would cause an infinite recursion and stack overflow. If we define a definition where the tail is not initially computable then we're going to have an infinite recursion:// The first time we try to access the tail we're going to need more // information which will require us to recurse, which will require us to // recurse, which... lazy val sov: Stream[Vector[Int]] = Vector(0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }The definition of
fibsabove creates a larger number of objects than necessary depending on how you might want to implement it. The following implementation provides a more "cost effective" implementation due to the fact that it has a more direct route to the numbers themselves:lazy val fib: Stream[Int] = { def loop(h: Int, n: Int): Stream[Int] = h #:: loop(n, h + n) loop(1, 1) }Note that
mkStringforces evaluation of aStream, butaddStringdoes not. In both cases, aStreamthat is or ends in a cycle (e.g.lazy val s: Stream[Int] = 0 #:: s) will convert additional trips through the cycle to.... Additionally,addStringwill display an un-memoized tail as?.the type of the elements contained in this stream.
2.8
"Scala's Collection Library overview" section on
Streamsfor more information.