This class implements an immutable linked list. We call it "lazy" because it computes its elements only when they are needed.
Elements are memoized; that is, the value of each element is computed at most once.
Elements are computed in-order and are never skipped. In other words, accessing the tail causes the head to be computed first.
How lazy is a LazyList? When you have a value of type LazyList, you
don't know yet whether the list is empty or not. If you learn that it is non-empty,
then you also know that the head has been computed. But the tail is itself
a LazyList, whose emptiness-or-not might remain undetermined.
A LazyList may be infinite. For example, LazyList.from(0) contains
all of the natural numbers 0, 1, 2, and so on. For infinite sequences,
some methods (such as count, sum, max or min) will not terminate.
Here is an example:
import scala.math.BigInt
object Main extends App {
val fibs: LazyList[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
// 3To illustrate, let's add some output to the definition fibs, so we
see what's going on.
import scala.math.BigInt
object Main extends App {
val fibs: LazyList[BigInt] =
BigInt(0) #:: BigInt(1) #::
fibs.zip(fibs.tail).map{ n =>
println(s"Adding ${n._1} and ${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
// 5Note that the definition of fibs uses val not def. The memoization of the
LazyList requires us to have somewhere to store the information and a val
allows us to do that.
Further remarks about the semantics of LazyList:
- Though the LazyList changes as it is accessed, this does not
contradict its immutability. Once the values are memoized they do
not change. Values that have yet to be memoized still "exist", they
simply haven't been computed yet.
- One must be cautious of memoization; it can eat up memory if you're not
careful. That's because memoization of the LazyList creates a structure much like
scala.collection.immutable.List. As long as something is holding on to
the head, the head holds on to the tail, and so on recursively.
If, on the other hand, there is nothing holding on to the head (e.g. if we used
def to define the LazyList) then once it is no longer being used directly,
it disappears.
- Note that some operations, including drop, dropWhile, flatMap or collect may process a large number of intermediate elements before returning.
Here's another example. Let's start with the natural numbers and iterate 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 LazyList definition will be a val definition
val lazylist1: LazyList[Int] = {
def loop(v: Int): LazyList[Int] = v #:: loop(v + 1)
loop(0)
}
// Because lazylist1 is a val, everything that the iterator produces is held
// by virtue of the fact that the head of the LazyList is held in lazylist1
val it1 = lazylist1.iterator
loop("Iterator1: ", it1.next(), it1)
// We can redefine this LazyList such that all we have is the Iterator left
// and allow the LazyList to be garbage collected as required. Using a def
// to provide the LazyList ensures that no val is holding onto the head as
// is the case with lazylist1
def lazylist2: LazyList[Int] = {
def loop(v: Int): LazyList[Int] = v #:: loop(v + 1)
loop(0)
}
val it2 = lazylist2.iterator
loop("Iterator2: ", it2.next(), it2)
// And, of course, we don't actually need a LazyList at all for such a simple
// problem. There's no reason to use a LazyList 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)- In the fibs example earlier, the fact that tail works at all is of interest.
fibs has an initial (0, 1, LazyList(...)), so tail is deterministic.
If we defined fibs such that only 0 were concretely known, then the act
of determining tail would require the evaluation of tail, so the
computation would be unable to progress, as in this code:
// 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: LazyList[Vector[Int]] = Vector(0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }The definition of fibs above 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: LazyList[Int] = {
def loop(h: Int, n: Int): LazyList[Int] = h #:: loop(n, h + n)
loop(1, 1)
}The head, the tail and whether the list is empty or not can be initially unknown.
Once any of those are evaluated, they are all known, though if the tail is
built with #:: or #:::, it's content still isn't evaluated. Instead, evaluating
the tails content is deferred until the tails empty status, head or tail is
evaluated.
Delaying the evaluation of whether a LazyList is empty or not until it's needed
allows LazyList to not eagerly evaluate any elements on a call to filter.
Only when it's further evaluated (which may be never!) any of the elements gets forced.
for example:
def tailWithSideEffect: LazyList[Nothing] = {
println("getting empty LazyList")
LazyList.empty
}
val emptyTail = tailWithSideEffect // prints "getting empty LazyList"
val suspended = 1 #:: tailWithSideEffect // doesn't print anything
val tail = suspended.tail // although the tail is evaluated, *still* nothing is yet printed
val filtered = tail.filter(_ => false) // still nothing is printed
filtered.isEmpty // prints "getting empty LazyList"- Type parameters:
- A
the type of the elements contained in this lazy list.
- See also:
"Scala's Collection Library overview" section on
LazyListsfor more information.- Companion:
- object
- Source:
- LazyList.scala
Value members
Concrete methods
Construct a LazyList consisting of a given first element followed by elements from another LazyList.
Construct a LazyList consisting of a given first element followed by elements from another LazyList.
- Source:
- LazyList.scala
Construct a LazyList consisting of the concatenation of the given LazyList and another LazyList.
Construct a LazyList consisting of the concatenation of the given LazyList and another LazyList.
- Source:
- LazyList.scala
Appends all elements of this lazy list to a string builder using start, end, and separator strings.
Appends all elements of this lazy list 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 lazy list are separated by the string sep.
An undefined state is represented with "<not computed>" and cycles are represented with "<cycle>".
This method evaluates all elements of the collection.
- Value parameters:
- end
the ending string.
- sb
the string builder to which elements are appended.
- sep
the separator string.
- start
the starting string.
- Returns:
the string builder
bto which elements were appended.- Definition Classes
- Source:
- LazyList.scala
A copy of this lazy list with an element appended.
A copy of this lazy list 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)This method preserves laziness; elements are only evaluated individually as needed.
Note: Repeated chaining of calls to append methods (appended,
appendedAll, lazyAppendedAll) without forcing any of the
intermediate resulting lazy lists may overflow the stack when
the final result is forced.
- Definition Classes
- Source:
- LazyList.scala
Returns a new lazy list containing the elements from the left hand operand followed by the elements from the right hand operand.
Returns a new lazy list containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the lazy list is the most specific superclass encompassing the element types of the two operands.
This method preserves laziness; elements are only evaluated individually as needed.
Note: Repeated chaining of calls to append methods (appended,
appendedAll, lazyAppendedAll) without forcing any of the
intermediate resulting lazy lists may overflow the stack when
the final result is forced.
- Definition Classes
- Source:
- LazyList.scala
Builds a new lazy list by applying a partial function to all elements of this lazy list on which the function is defined.
Builds a new lazy list by applying a partial function to all elements of this lazy list on which the function is defined.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Finds the first element of the lazy list for which the given partial function is defined, and applies the partial function to it.
Finds the first element of the lazy list for which the given partial function is defined, and applies the partial function to it.
Note: may not terminate for infinite-sized collections.
This method does not evaluate any elements further than the first element for which the partial function is defined.
- Definition Classes
- Source:
- LazyList.scala
Computes the multiset difference between this lazy list and another sequence.
Computes the multiset difference between this lazy list and another sequence.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Selects all elements except first n ones.
Selects all elements except first n ones.
This method does not evaluate anything until an operation is performed
on the result (e.g. calling head or tail, or checking if it is empty).
Additionally, it preserves laziness for all except the first n elements.
- Definition Classes
- Source:
- LazyList.scala
Selects all elements except last n ones.
Selects all elements except last n ones.
This method does not evaluate anything until an operation is performed
on the result (e.g. calling head or tail, or checking if it is empty).
- Definition Classes
- Source:
- LazyList.scala
Drops longest prefix of elements that satisfy a predicate.
Drops longest prefix of elements that satisfy a predicate.
This method does not evaluate anything until an operation is performed
on the result (e.g. calling head or tail, or checking if it is empty).
Additionally, it preserves laziness for all elements after the predicate returns false.
- Definition Classes
- Source:
- LazyList.scala
Selects all elements of this lazy list which satisfy a predicate.
Selects all elements of this lazy list which satisfy a predicate.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Selects all elements of this lazy list which do not satisfy a predicate.
Selects all elements of this lazy list which do not satisfy a predicate.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Finds the first element of the lazy list satisfying a predicate, if any.
Finds the first element of the lazy list satisfying a predicate, if any.
Note: may not terminate for infinite-sized collections.
This method does not evaluate any elements further than the first element matching the predicate.
- Definition Classes
- Source:
- LazyList.scala
Builds a new lazy list by applying a function to all elements of this lazy list and using the elements of the resulting collections.
Builds a new lazy list by applying a function to all elements of this lazy 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 lazy 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)This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Converts this lazy list of traversable collections into a lazy list formed by the elements of these traversable collections.
Converts this lazy list of traversable collections into a lazy list formed by the elements of these traversable collections.
The resulting collection's type will be guided by the type of lazy list. 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)This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
LazyList specialization of foldLeft which allows GC to collect along the way.
LazyList specialization of foldLeft which allows GC to collect along the way.
- Type parameters:
- B
The type of value being accumulated.
- Value parameters:
- op
The operation to perform on successive elements of the
LazyList.- z
The initial value seeded into the function
op.
- Returns:
The accumulated value from successive applications of
op.- Definition Classes
- Source:
- LazyList.scala
Evaluates all undefined elements of the lazy list.
Evaluates all undefined elements of the lazy list.
This method detects cycles in lazy lists, and terminates after all elements of the cycle are evaluated. For example:
val ring: LazyList[Int] = 1 #:: 2 #:: 3 #:: ring
ring.force
ring.toString
// prints
//
// LazyList(1, 2, 3, ...)This method will *not* terminate for non-cyclic infinite-sized collections.
- Returns:
this
- Source:
- LazyList.scala
Apply the given function f to each element of this linear sequence
(while respecting the order of the elements).
Apply the given function f to each element of this linear sequence
(while respecting the order of the elements).
- Value parameters:
- f
The treatment to apply to each element.
- Note:
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 LazyList as elements are consumed.
This function will force the realization of the entire LazyList unless the
fthrows an exception.- Definition Classes
- Source:
- LazyList.scala
Partitions elements in fixed size lazy lists.
Partitions elements in fixed size lazy lists.
The iterator returned by this method mostly preserves laziness; a single element ahead of the iterator is evaluated.
- Definition Classes
- Source:
- LazyList.scala
Computes the multiset intersection between this lazy list and another sequence.
Computes the multiset intersection between this lazy list and another sequence.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Iterator can be used only once
Iterator can be used only once
The iterator returned by this method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
This method preserves laziness; elements are only evaluated individually as needed.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
The lazy list resulting from the concatenation of this lazy list with the argument lazy list.
The lazy list resulting from the concatenation of this lazy list with the argument lazy list.
This method preserves laziness; elements are only evaluated individually as needed.
Note: Repeated chaining of calls to append methods (appended,
appendedAll, lazyAppendedAll) without forcing any of the
intermediate resulting lazy lists may overflow the stack when
the final result is forced.
- Value parameters:
- suffix
The collection that gets appended to this lazy list
- Returns:
The lazy list containing elements of this lazy list and the iterable object.
- Source:
- LazyList.scala
Analogous to zip except that the elements in each collection are not consumed until a strict operation is
invoked on the returned LazyZip2 decorator.
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)This method is not particularly useful for a lazy list, as zip already preserves laziness.
The collection.LazyZip2 returned by this method preserves laziness; elements are
only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Builds a new lazy list by applying a function to all elements of this lazy list.
Builds a new lazy list by applying a function to all elements of this lazy list.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
A copy of this lazy list with an element value appended until a given target length is reached.
A copy of this lazy list with an element value appended until a given target length is reached.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
A pair of, first, all elements that satisfy predicate p and, second,
all elements that do not.
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.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Applies a function f to each element of the lazy list and returns a pair of lazy lists: 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.
Applies a function f to each element of the lazy list and returns a pair of lazy lists: 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 = `LazyList`(1, "one", 2, "two", 3, "three") partitionMap {
case i: Int => Left(i)
case s: String => Right(s)
}
// xs == (`LazyList`(1, 2, 3),
// `LazyList`(one, two, three))This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Produces a new lazy list where a slice of elements in this lazy list is replaced by another sequence.
Produces a new lazy list where a slice of elements in this lazy list 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 lazy list appends the patch to the end. If more values are replaced than actually exist, the excess is ignored.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
A copy of the lazy list with an element prepended.
A copy of the lazy list with an element prepended.
Also, the original lazy 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)This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
As with :++, returns a new collection containing the elements from the left operand followed by the
elements from the right operand.
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.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
LazyList specialization of reduceLeft which allows GC to collect along the way.
LazyList specialization of reduceLeft which allows GC to collect along the way.
- Type parameters:
- B
The type of value being accumulated.
- Value parameters:
- f
The operation to perform on successive elements of the
LazyList.
- Returns:
The accumulated value from successive applications of
f.- Definition Classes
- Source:
- LazyList.scala
Returns new lazy list with elements in reversed order.
Returns new lazy list with elements in reversed order.
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.
This method evaluates all elements of the collection.
- Definition Classes
- Source:
- LazyList.scala
Produces a lazy list containing cumulative results of applying the operator going left to right, including the initial value.
Produces a lazy list containing cumulative results of applying the operator going left to right, including the initial value.
Note: will not terminate for infinite-sized collections.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Selects an interval of elements.
Selects an interval of elements. The returned lazy list is made up
of all elements x which satisfy the invariant:
from <= indexOf(x) < untilThis method does not evaluate anything until an operation is performed
on the result (e.g. calling head or tail, or checking if it is empty).
Additionally, it preserves laziness for all but the first from elements.
- Definition Classes
- Source:
- LazyList.scala
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)
The returned iterator will be empty when called on an empty collection. The last element the iterator produces may be smaller than the window size when the original collection isn't exhausted by the window before it and its last element isn't skipped by the step before it.
The iterator returned by this method mostly preserves laziness;
size - step max 1 elements ahead of the iterator are evaluated.
- Definition Classes
- Source:
- LazyList.scala
Selects the first n elements.
Selects the first n elements.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Selects the last n elements.
Selects the last n elements.
This method does not evaluate anything until an operation is performed
on the result (e.g. calling head or tail, or checking if it is empty).
- Definition Classes
- Source:
- LazyList.scala
Takes longest prefix of elements that satisfy a predicate.
Takes longest prefix of elements that satisfy a predicate.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Applies a side-effecting function to each element in this collection.
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.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
This method preserves laziness; elements are only evaluated individually as needed.
This method preserves laziness; elements are only evaluated individually as needed.
- Returns:
a string representation of this collection. An undefined state is represented with
"<not computed>"and cycles are represented with"<cycle>"Examples:"LazyList(4, <not computed>)", a non-empty lazy list ;"LazyList(1, 2, 3, <not computed>)", a lazy list with at least three elements ;"LazyList(1, 2, 3, <cycle>)", an infinite lazy list that contains a cycle at the fourth element.
- Definition Classes
- Source:
- LazyList.scala
Transposes this lazy list of iterable collections into a lazy list of lazy lists.
Transposes this lazy list of iterable collections into a lazy list of lazy lists.
The resulting collection's type will be guided by the static type of lazy list. 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.
This method evaluates all elements of the collection.
- Definition Classes
- Source:
- LazyList.scala
Converts this lazy list of pairs into two collections of the first and second half of each pair.
Converts this lazy list of pairs into two collections of the first and second half of each pair.
val xs = `LazyList`(
(1, "one"),
(2, "two"),
(3, "three")).unzip
// xs == (`LazyList`(1, 2, 3),
// `LazyList`(one, two, three))This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Converts this lazy list of triples into three collections of the first, second, and third element of each triple.
Converts this lazy list of triples into three collections of the first, second, and third element of each triple.
val xs = `LazyList`(
(1, "one", '1'),
(2, "two", '2'),
(3, "three", '3')).unzip3
// xs == (`LazyList`(1, 2, 3),
// `LazyList`(one, two, three),
// `LazyList`(1, 2, 3))This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
A copy of this lazy list with one single replaced element.
A copy of this lazy list with one single replaced element.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
A collection.WithFilter which allows GC of the head of lazy list during processing.
A collection.WithFilter which allows GC of the head of lazy list during processing.
This method is not particularly useful for a lazy list, as filter already preserves laziness.
The collection.WithFilter returned by this method preserves laziness; elements are
only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs.
Returns a lazy list formed from this lazy list 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.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs.
Returns a lazy list formed from this lazy list 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.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Zips this lazy list with its indices.
Zips this lazy list with its indices.
This method preserves laziness; elements are only evaluated individually as needed.
- Definition Classes
- Source:
- LazyList.scala
Deprecated methods
Tests whether this lazy list is known to have a finite size.
Tests whether this lazy list 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.
This method preserves laziness; elements are only evaluated individually as needed.
- Deprecated
- Definition Classes
- Source:
- LazyList.scala
Inherited methods
Appends all elements of this collection to a string builder.
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- Value parameters:
- b
the string builder to which elements are appended.
- Returns:
the string builder
bto which elements were appended.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Appends all elements of this collection to a string builder using a separator string.
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- Value parameters:
- b
the string builder to which elements are appended.
- sep
the separator string.
- Returns:
the string builder
bto which elements were appended.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Composes this partial function with another partial function that gets applied to results of this partial function.
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. For efficiency, it is recommended to call applyOrElse instead of isDefinedAt or apply.
- Type parameters:
- C
the result type of the transformation function.
- Value parameters:
- k
the transformation function
- Returns:
a partial function with the domain of this partial function narrowed by other partial function, which maps arguments
xtok(this(x)).- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Composes this partial function with a transformation function that gets applied to results of this partial function.
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).
- Type parameters:
- C
the result type of the transformation function.
- Value parameters:
- k
the transformation function
- Returns:
a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments
xtok(this(x)).- Definition Classes
- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
- Definition Classes
- Inherited from:
- LinearSeqOps
- Source:
- LinearSeq.scala
Applies this partial function to the given argument when it is contained in the function domain.
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.
- Value parameters:
- default
the fallback function
- x
the function argument
- Returns:
the result of this function or fallback function application.
- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Iterates over combinations.
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.
Composes another partial function k with this partial function so that this
partial function gets applied to results of k.
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. For efficiency, it is recommended to call applyOrElse instead of isDefinedAt or apply.
- Type parameters:
- R
the parameter type of the transformation function.
- Value parameters:
- k
the transformation function
- Returns:
a partial function with the domain of other partial function narrowed by this partial function, which maps arguments
xtothis(k(x)).- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Composes two instances of Function1 in a new Function1, with this function applied last.
Composes two instances of Function1 in a new Function1, with this function applied last.
- Type parameters:
- A
the type to which function
gcan be applied
- Value parameters:
- g
a function A => T1
- Returns:
a new function
fsuch thatf(x) == apply(g(x))- Inherited from:
- Function1
- Source:
- Function1.scala
Copy elements to an array, returning the number of elements written.
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.
- Type parameters:
- B
the type of the elements of the array.
- Value parameters:
- len
the maximal number of elements to copy.
- start
the starting index of xs.
- xs
the array to fill.
- Returns:
the number of elements written to the array
- Note:
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Copy elements to an array, returning the number of elements written.
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.
- Type parameters:
- B
the type of the elements of the array.
- Value parameters:
- start
the starting index of xs.
- xs
the array to fill.
- Returns:
the number of elements written to the array
- Note:
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Copy elements to an array, returning the number of elements written.
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.
- Type parameters:
- B
the type of the elements of the array.
- Value parameters:
- xs
the array to fill.
- Returns:
the number of elements written to the array
- Note:
Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.
Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
the type of the elements of
that
- Value parameters:
- p
the test predicate, which relates elements from both collections
- that
the other collection
- Returns:
trueif both collections have the same length andp(x, y)istruefor all corresponding elementsxof this iterator andyofthat, otherwisefalse- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.
Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.
- Type parameters:
- B
the type of the elements of
that
- Value parameters:
- p
the test predicate, which relates elements from both sequences
- that
the other sequence
- Returns:
trueif both sequences have the same length andp(x, y)istruefor all corresponding elementsxof this sequence andyofthat, otherwisefalse.- Inherited from:
- SeqOps
- Source:
- Seq.scala
Counts the number of elements in the collection which satisfy a predicate.
Counts the number of elements in the collection which satisfy a predicate.
Note: will not terminate for infinite-sized collections.
- Value parameters:
- p
the predicate used to test elements.
- Returns:
the number of elements satisfying the predicate
p.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Selects all the elements of this sequence ignoring the duplicates as determined by == after applying
the transforming function f.
Selects all the elements of this sequence ignoring the duplicates as determined by == after applying
the transforming function f.
- Type parameters:
- B
the type of the elements after being transformed by
f
- Value parameters:
- f
The transforming function whose result is used to determine the uniqueness of each element
- Returns:
a new sequence consisting of all the elements of this sequence without duplicates.
- Inherited from:
- SeqOps
- Source:
- Seq.scala
Returns an extractor object with a unapplySeq method, which extracts each element of a sequence data.
Returns an extractor object with a unapplySeq method, which extracts each element of a sequence data.
- 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 }- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Folds the elements of this collection using the specified associative binary operator.
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.
- Type parameters:
- A1
a type parameter for the binary operator, a supertype of
A.
- Value parameters:
- op
a binary operator that must be associative.
- 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.,
Nilfor list concatenation, 0 for addition, or 1 for multiplication).
- Returns:
the result of applying the fold operator
opbetween all the elements andz, orzif this collection is empty.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Applies a binary operator to all elements of this collection and a start value, going right to left.
Applies a binary operator to all elements of this collection and a start value, 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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- z
the start value.
- Returns:
the result of inserting
opbetween consecutive elements of this collection, going right to left with the start valuezon the right:op(x1, op(x2, ... op(xn, z)...))wherex1, ..., xnare the elements of this collection. Returnszif this collection is empty.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Partitions this iterable collection into a map of iterable collections according to some discriminator function.
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.
- Type parameters:
- K
the type of keys returned by the discriminator function.
- Value parameters:
- 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
kis bound to a iterable collection of those elementsxfor whichf(x)equalsk.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Partitions this iterable collection into a map of iterable collections according to a discriminator function key.
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.
- Type parameters:
- B
the type of values returned by the transformation function
- K
the type of keys returned by the discriminator function
- Value parameters:
- f
the element transformation function
- key
the discriminator function
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Partitions this iterable collection into a map according to a discriminator function key.
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 f 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.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Finds index of first occurrence of some value in this sequence.
Finds index of first occurrence of some value in this sequence.
Finds index of first occurrence of some value in this sequence after or at some start index.
Finds index of first occurrence of some value in this sequence after or at some start index.
Finds first index where this sequence contains a given sequence as a slice.
Finds first index where this sequence contains a given sequence as a slice.
Note: may not terminate for infinite-sized collections.
Finds first index after or at a start index where this sequence contains a given sequence as a slice.
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.
Finds index of the first element satisfying some predicate.
Finds index of the first element satisfying some predicate.
Note: may not terminate for infinite-sized collections.
The initial part of the collection without its last element.
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.
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Iterates over the inits of this iterable collection.
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
- Example:
List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Finds index of last occurrence of some value in this sequence before or at a given end index.
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.
Finds last index where this sequence contains a given sequence as a slice.
Finds last index where this sequence contains a given sequence as a slice.
Note: will not terminate for infinite-sized collections.
Finds last index before or at a given end index where this sequence contains a given sequence as a slice.
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.
Finds index of last element satisfying some predicate.
Finds index of last element satisfying some predicate.
Note: will not terminate for infinite-sized collections.
Optionally selects the last element.
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,
Noneif it is empty.- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Returns a value class containing operations for comparing the length of this sequence to a test value.
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) > 0Turns this partial function into a plain function returning an Option result.
Turns this partial function into a plain function returning an Option result.
- Returns:
a function that takes an argument
xtoSome(this(x))ifthisis defined forx, and toNoneotherwise.- See also:
Function.unlift
- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Finds the largest element.
Finds the largest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- ord
An ordering to be used for comparing elements.
- Returns:
the largest element of this collection with respect to the ordering
ord.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the largest value measured by function f.
Finds the first element which yields the largest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- Returns:
the first element of this collection with the largest value measured by function f with respect to the ordering
cmp.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the largest value measured by function f.
Finds the first element which yields the largest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- 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.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the largest element.
Finds the largest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- 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.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the smallest element.
Finds the smallest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- ord
An ordering to be used for comparing elements.
- Returns:
the smallest element of this collection with respect to the ordering
ord.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the smallest value measured by function f.
Finds the first element which yields the smallest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- Returns:
the first element of this collection with the smallest value measured by function f with respect to the ordering
cmp.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the first element which yields the smallest value measured by function f.
Finds the first element which yields the smallest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The result type of the function f.
- Value parameters:
- cmp
An ordering to be used for comparing elements.
- f
The measuring function.
- 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.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Finds the smallest element.
Finds the smallest element.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
The type over which the ordering is defined.
- Value parameters:
- 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.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Displays all elements of this collection in a 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.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Displays all elements of this collection in a string using a separator string.
Displays all elements of this collection in a string using a separator string.
Delegates to addString, which can be overridden.
- Value parameters:
- 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 stringsep.- Example:
List(1, 2, 3).mkString("|") = "1|2|3"- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Displays all elements of this collection in a string using start, end, and separator strings.
Displays all elements of this collection in a string using start, end, and separator strings.
Delegates to addString, which can be overridden.
- Value parameters:
- end
the ending string.
- sep
the separator string.
- start
the starting string.
- Returns:
a string representation of this collection. The resulting string begins with the string
startand ends with the stringend. Inside, the string representations (w.r.t. the methodtoString) of all elements of this collection are separated by the stringsep.- Example:
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tests whether the collection is not empty.
Tests whether the collection is not empty.
- Returns:
trueif the collection contains at least one element,falseotherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.
- Type parameters:
- A1
the argument type of the fallback function
- B1
the result type of the fallback function
- Value parameters:
- 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 takesxtothis(x)wherethisis defined, and tothat(x)where it is not.- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Multiplies up the elements of this collection.
Multiplies up the elements of this collection.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
the result type of the
*operator.
- Value parameters:
- 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 innum.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Reduces the elements of this collection using the specified associative binary operator.
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.
- Type parameters:
- B
A type parameter for the binary operator, a supertype of
A.
- Value parameters:
- op
A binary operator that must be associative.
- Returns:
The result of applying reduce operator
opbetween all the elements if the collection is nonempty.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Optionally applies a binary operator to all elements of this collection, going left to right.
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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
an option value containing the result of
reduceLeft(op)if this collection is nonempty,Noneotherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Reduces the elements of this collection, if any, using the specified associative binary operator.
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.
- Type parameters:
- B
A type parameter for the binary operator, a supertype of
A.
- Value parameters:
- op
A binary operator that must be associative.
- Returns:
An option value containing result of applying reduce operator
opbetween all the elements if the collection is nonempty, andNoneotherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Applies a binary operator to all elements of this collection, going right to left.
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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
the result of inserting
opbetween consecutive elements of this collection, going right to left:op(x1, op(x2, ..., op(xn-1, xn)...))wherex1, ..., xnare the elements of this collection.- Throws:
- UnsupportedOperationException
if this collection is empty.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Optionally applies a binary operator to all elements of this collection, going right to left.
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.
- Type parameters:
- B
the result type of the binary operator.
- Value parameters:
- op
the binary operator.
- Returns:
an option value containing the result of
reduceRight(op)if this collection is nonempty,Noneotherwise.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
An iterator yielding elements in reversed order.
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.
Composes this partial function with an action function which gets applied to results of this partial function.
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 falseexcept 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.
- Value parameters:
- action
the action function
- Returns:
a function which maps arguments
xtoisDefinedAt(x). The resulting function runsaction(this(x))wherethisis defined.- See also:
applyOrElse.- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Computes a prefix scan of the elements of the collection.
Computes a prefix scan of the elements of the collection.
Note: The neutral element z may be applied more than once.
- Type parameters:
- B
element type of the resulting collection
- Value parameters:
- op
the associative operator for the scan
- z
neutral element for the operator
op
- Returns:
a new iterable collection containing the prefix scan of the elements in this iterable collection
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Produces a collection containing cumulative results of applying the operator going right to left.
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)- Type parameters:
- B
the type of the elements in the resulting collection
- Value parameters:
- op
the binary operator applied to the intermediate result and the element
- z
the initial value
- Returns:
collection with intermediate results
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Search within an interval in this sorted sequence for a specific element.
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.
- Value parameters:
- elem
the element to find.
- from
the index where the search starts.
- ord
the ordering to be used to compare elements.
- to
the index following where the search ends.
- Returns:
a
Foundvalue containing the index corresponding to the element in the sequence, or theInsertionPointwhere the element would be inserted if the element is not in the sequence.- See also:
- Note:
if
to <= from, the search space is empty, and anInsertionPointatfromis returned- Inherited from:
- SeqOps
- Source:
- Seq.scala
Search this sorted sequence for a specific element.
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.
- Value parameters:
- elem
the element to find.
- ord
the ordering to be used to compare elements.
- Returns:
a
Foundvalue containing the index corresponding to the element in the sequence, or theInsertionPointwhere the element would be inserted if the element is not in the sequence.- See also:
- Inherited from:
- SeqOps
- Source:
- Seq.scala
Computes the length of the longest segment that starts from the first element and whose elements all satisfy some predicate.
Computes the length of the longest segment that starts from the first element and whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
Returns a value class containing operations for comparing the size of this iterable collection to a test value.
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- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Groups elements in fixed size blocks by passing a "sliding window"
over them (as opposed to partitioning them, as is done in grouped.)
Groups elements in fixed size blocks by passing a "sliding window"
over them (as opposed to partitioning them, as is done in grouped.)
An empty collection returns an empty iterator, and a non-empty collection containing fewer elements than the window size returns an iterator that will produce the original collection as its only element.
- Value parameters:
- size
the number of elements per group
- Returns:
An iterator producing iterable collections of size
size, except for a non-empty collection with less thansizeelements, which returns an iterator that produces the source collection itself as its only element.- See also:
scala.collection.Iterator, method
sliding- Example:
List().sliding(2) = empty iteratorList(1).sliding(2) = Iterator(List(1))List(1, 2).sliding(2) = Iterator(List(1, 2))List(1, 2, 3).sliding(2) = Iterator(List(1, 2), List(2, 3))- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Sorts this sequence according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.
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.
- Type parameters:
- B
the target type of the transformation
f, and the type where the orderingordis defined.
- Value parameters:
- 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 < yiford.lt(f(x), f(y)).- See also:
- 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)- Inherited from:
- SeqOps
- Source:
- Seq.scala
Sorts this sequence according to a comparison function.
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.
- Value parameters:
- 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.- Example:
List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) = List("Bob", "John", "Steve", "Tom")- Inherited from:
- SeqOps
- Source:
- Seq.scala
Sorts this sequence according to an Ordering.
Sorts this 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.
- Value parameters:
- ord
the ordering to be used to compare elements.
- Returns:
a sequence consisting of the elements of this sequence sorted according to the ordering
ord.- See also:
scala.math.Ordering Note: Even when applied to a view or a lazy collection it will always force the elements.
- Inherited from:
- SeqOps
- Source:
- Seq.scala
Tests whether this sequence contains the given sequence at a given index.
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.
Returns a scala.collection.Stepper for the elements of this collection.
Returns a scala.collection.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 scala.collection.StepperShape parameter defines the resulting Stepper type according to the element type of this collection.
For collections of
Int,Short,ByteorChar, an scala.collection.IntStepper is returnedFor collections of
DoubleorFloat, a scala.collection.DoubleStepper is returnedFor collections of
Longa scala.collection.LongStepper is returnedFor any other element type, an scala.collection.AnyStepper is returned
Note that this method is overridden in subclasses and the return type is refined to
S with EfficientSplit, for example scala.collection.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.
- Inherited from:
- IterableOnce
- Source:
- IterableOnce.scala
Sums up the elements of this collection.
Sums up the elements of this collection.
Note: will not terminate for infinite-sized collections.
- Type parameters:
- B
the result type of the
+operator.
- Value parameters:
- 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 innum.- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Given a collection factory factory, convert this collection to the appropriate
representation for the current element type A.
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]
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Convert collection to array.
Convert collection to array.
Implementation note: DO NOT call Array.from from this method.
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Tries to extract a B from an A in a pattern matching expression.
Tries to extract a B from an A in a pattern matching expression.
- Inherited from:
- PartialFunction
- Source:
- PartialFunction.scala
Deprecated and Inherited methods
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Returns the length of the longest prefix whose elements all satisfy some predicate.
Returns the length of the longest prefix whose elements all satisfy some predicate.
Note: may not terminate for infinite-sized collections.
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- Iterable
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- Iterable
- Source:
- Iterable.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
- Deprecated
- Inherited from:
- IterableOnceOps
- Source:
- IterableOnce.scala
Converts this iterable collection to an unspecified Iterable.
Converts this iterable collection to an unspecified Iterable. Will return the same collection if this instance is already Iterable.
- Returns:
An Iterable containing all elements of this iterable collection.
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala
Produces a new sequence which contains all elements of this sequence and also all elements of a given sequence.
Produces a new sequence which contains all elements of this sequence and also all elements of
a given sequence. xs union ys is equivalent to xs ++ ys.
A view over a slice of the elements of this collection.
A view over a slice of the elements of this collection.
- Deprecated
- Inherited from:
- IterableOps
- Source:
- Iterable.scala