Scala 3/scala/scala.collection/scala.collection.immutable/Queue

Queue

scala.collection.immutable.Queue

See theQueue companion object

sealed class Queue[+A] extends AbstractSeq[A], LinearSeq[A], LinearSeqOps[A, Queue, Queue[A]], StrictOptimizedLinearSeqOps[A, Queue, Queue[A]], StrictOptimizedSeqOps[A, Queue, Queue[A]], IterableFactoryDefaults[A, Queue], DefaultSerializable

Queue objects implement data structures that allow to insert and retrieve elements in a first-in-first-out (FIFO) manner.

Queue is implemented as a pair of Lists, one containing the in elements and the other the out elements. Elements are added to the in list and removed from the out list. When the out list runs dry, the queue is pivoted by replacing the out list by in.reverse, and in by Nil.

Adding items to the queue always has cost O(1). Removing items has cost O(1), except in the case where a pivot is required, in which case, a cost of O(n) is incurred, where n is the number of elements in the queue. When this happens, n remove operations with O(1) cost are guaranteed. Removing an item is on average O(1).

Attributes

See also: "Scala's Collection Library overview" section on Immutable Queues for more information.
Companion: object
Source: Queue.scala
Graph
Supertypes: trait DefaultSerializable

trait Serializable

trait StrictOptimizedSeqOps[A, Queue, Queue[A]]

trait StrictOptimizedLinearSeqOps[A, Queue, Queue[A]]

trait StrictOptimizedSeqOps[A, Queue, Queue[A]]

trait StrictOptimizedIterableOps[A, Queue, Queue[A]]

trait LinearSeq[A]

trait LinearSeqOps[A, Queue, Queue[A]]

trait LinearSeq[A]

trait LinearSeqOps[A, Queue, Queue[A]]

class AbstractSeq[A]

trait Seq[A]

trait SeqOps[A, Queue, Queue[A]]

trait Iterable[A]

class AbstractSeq[A]

trait Seq[A]

trait Equals

trait SeqOps[A, Queue, Queue[A]]

trait PartialFunction[Int, A]

trait Int => A

class AbstractIterable[A]

trait Iterable[A]

trait IterableFactoryDefaults[A, Queue]

trait IterableOps[A, Queue, Queue[A]]

trait IterableOnceOps[A, Queue, Queue[A]]

trait IterableOnce[A]

class Object

trait Matchable

class Any
Show all

Members list

Value members

Concrete methods

A copy of this immutable queue with an element appended.

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)

Type parameters

B: the element type of the returned immutable queue.

Value parameters

elem: the appended element

Attributes

Returns: a new immutable queue consisting of all elements of this immutable queue followed by value.
Definition Classes: StrictOptimizedSeqOps -> SeqOps
Source: Queue.scala

Returns a new immutable queue containing the elements from the left hand operand followed by the elements from the right hand operand.

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

Type parameters

B: the element type of the returned collection.

Value parameters

suffix: the iterable to append.

Attributes

Returns: a new collection of type CC[B] which contains all elements of this immutable queue followed by all elements of suffix.
Definition Classes: StrictOptimizedSeqOps -> SeqOps
Source: Queue.scala

Returns the n-th element of this queue.

Returns the n-th element of this queue. The first element is at position 0.

Value parameters

n: index of the element to return

Attributes

Returns: the element at position n in this queue.
Throws: NoSuchElementException if the queue is too short.
Definition Classes: LinearSeqOps -> SeqOps -> Function1
Source: Queue.scala

Returns a tuple with the first element in the queue, and a new queue with this element removed.

Attributes

Returns: the first element of the queue.
Throws: NoSuchElementException if the queue is empty
Source: Queue.scala

Optionally retrieves the first element and a queue of the remaining elements.

Attributes

Returns: A tuple of the first element of the queue, and a new queue with this element removed. If the queue is empty, None is returned.
Source: Queue.scala

Creates a new queue with element added at the end of the old queue.

Value parameters

elem: the element to insert

Attributes

Source: Queue.scala

Creates a new queue with all elements provided by an Iterable object added at the end of the old queue.

The elements are appended in the order they are given out by the iterator.

Value parameters

iter: an iterable object

Attributes

Source: Queue.scala

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

Value parameters

p: the predicate used to test elements.

Attributes

Returns: true if the given predicate p is satisfied by at least one element of this immutable queue, otherwise false
Definition Classes: LinearSeqOps -> IterableOnceOps
Source: Queue.scala

Tests whether a predicate holds for all elements of this immutable queue.

Value parameters

p: the predicate used to test elements.

Attributes

Returns: true if this immutable queue is empty or the given predicate p holds for all elements of this immutable queue, otherwise false.
Definition Classes: LinearSeqOps -> IterableOnceOps
Source: Queue.scala

Returns the first element in the queue, or throws an error if there is no element contained in the queue.

Attributes

Returns: the first element.
Throws: NoSuchElementException if the queue is empty
Source: Queue.scala

Selects the first element of this immutable queue.

Note: *Must* be overridden in subclasses. The default implementation is inherited from IterableOps.

Attributes

Definition Classes: LinearSeqOps -> IterableOps
Source: Queue.scala

Checks if the queue is empty.

Attributes

Returns: true, iff there is no element in the queue.
Definition Classes: LinearSeqOps -> SeqOps -> IterableOnceOps
Source: Queue.scala

The companion object of this immutable queue, providing various factory methods.

Attributes

Note: When implementing a custom collection type and refining CC to the new type, this method needs to be overridden to return a factory for the new type (the compiler will issue an error otherwise).
Definition Classes: LinearSeq -> LinearSeq -> Seq -> Iterable -> Seq -> Iterable -> IterableOps
Source: Queue.scala

Returns the elements in the list as an iterator

Attributes

Definition Classes: StrictOptimizedLinearSeqOps -> LinearSeqOps -> IterableOnce
Source: Queue.scala

Selects the last element.

Attributes

Returns: The last element of this immutable queue.
Throws: NoSuchElementException If the immutable queue is empty.
Definition Classes: LinearSeqOps -> IterableOps
Source: Queue.scala

Returns the length of the queue.

Attributes

Definition Classes: LinearSeqOps -> SeqOps
Source: Queue.scala

A copy of the immutable queue with an element prepended.

Also, the original immutable queue 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)

Type parameters

B: the element type of the returned immutable queue.

Value parameters

elem: the prepended element

Attributes

Returns: a new immutable queue consisting of value followed by all elements of this immutable queue.
Definition Classes: StrictOptimizedSeqOps -> SeqOps
Source: Queue.scala

The rest of the collection without its first element.

Note: *Must* be overridden in subclasses. The default implementation is inherited from IterableOps.

Attributes

Definition Classes: LinearSeqOps -> IterableOps
Source: Queue.scala

Returns a string representation of this queue.

Attributes

Definition Classes: Seq -> Function1 -> Iterable -> Any
Source: Queue.scala

Deprecated methods

Creates a new queue with all elements provided by an Iterable object added at the end of the old queue.

The elements are appended in the order they are given out by the iterator.

Value parameters

iter: an iterable object

Attributes

Deprecated: [Since version 2.13.0] Use `enqueueAll` instead of `enqueue` to enqueue a collection of elements
Source: Queue.scala

Inherited methods

Alias for concat

Attributes

Inherited from:: IterableOps
Source: Iterable.scala

Alias for prependedAll.

Attributes

Definition Classes: SeqOps -> IterableOps
Inherited from:: SeqOps
Source: Seq.scala

Alias for prepended.

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

Attributes

Inherited from:: SeqOps
Source: Seq.scala

Alias for appended.

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

Attributes

Inherited from:: SeqOps
Source: Seq.scala

Alias for appendedAll.

Attributes

Inherited from:: SeqOps
Source: Seq.scala

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.

Attributes

Returns: the string builder b to 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.

Attributes

Returns: the string builder b to which elements were appended.
Inherited from:: IterableOnceOps
Source: IterableOnce.scala

Appends all elements of this collection to a string builder using start, end, and separator strings.

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

Example:

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

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

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

Value parameters

b: the string builder to which elements are appended.
end: the ending string.
sep: the separator string.
start: the starting string.

Attributes

Returns: the string builder b to 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.

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

Attributes

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

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

Attributes

Returns: a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments x to k(this(x)).
Definition Classes: PartialFunction -> Function1
Inherited from:: PartialFunction
Source: PartialFunction.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

Attributes

Returns: the result of this function or fallback function application.
Inherited from:: PartialFunction
Source: PartialFunction.scala

Checks whether this instance can possibly equal that.

A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

Value parameters

that: the value being probed for possible equality

Attributes

Returns: true if this instance can possibly equal that, otherwise false
Inherited from:: Seq
Source: Seq.scala

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

Type parameters

B: the element type of the returned iterable collection.

Value parameters

pf: the partial function which filters and maps the iterable collection.

Attributes

Returns: a new iterable collection resulting from applying the given partial function pf to each element on which it is defined and collecting the results. The order of the elements is preserved.
Definition Classes: StrictOptimizedIterableOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedIterableOps
Source: StrictOptimizedIterableOps.scala

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

Note: may not terminate for infinite-sized collections.

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

Value parameters

pf: the partial function

Attributes

Returns: an option value containing pf applied to the first value for which it is defined, or None if none exists.
Example: Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
Inherited from:: IterableOnceOps
Source: IterableOnce.scala

Iterates over combinations of elements.

A combination of length n is a sequence of n elements selected in order of their first index in this sequence.

For example, "xyx" has two combinations of length 2. The x is selected first: "xx", "xy". The sequence "yx" is not returned as a combination because it is subsumed by "xy".

If there is more than one way to generate the same combination, only one will be returned.

For example, the result "xy" arbitrarily selected one of the x elements.

As a further illustration, "xyxx" has three different ways to generate "xy" because there are three elements x to choose from. Moreover, there are three unordered pairs "xx" but only one is returned.

It is not specified which of these equal combinations is returned. It is an implementation detail that should not be relied on. For example, the combination "xx" does not necessarily contain the first x in this sequence. This behavior is observable if the elements compare equal but are not identical.

As a consequence, "xyx".combinations(3).next() is "xxy": the combination does not reflect the order of the original sequence, but the order in which elements were selected, by "first index"; the order of each x element is also arbitrary.

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

Attributes

Returns

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

Example

Seq('a', 'b', 'b', 'b', 'c').combinations(2).foreach(println)
// List(a, b)
// List(a, c)
// List(b, b)
// List(b, c)
Seq('b', 'a', 'b').combinations(2).foreach(println)
// List(b, b)
// List(b, a)

Inherited from:

SeqOps

Source

Seq.scala

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

Type parameters

R: the parameter type of the transformation function.

Value parameters

k: the transformation function

Attributes

Returns: a partial function with the domain of other partial function narrowed by this partial function, which maps arguments x to this(k(x)).
Inherited from:: PartialFunction
Source: PartialFunction.scala

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

Type parameters

A: the type to which function g can be applied

Value parameters

g: a function A => T1

Attributes

Returns: a new function f such that f(x) == apply(g(x))
Inherited from:: Function1
Source: Function1.scala

Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand.

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

Type parameters

B: the element type of the returned collection.

Value parameters

suffix: the iterable to append.

Attributes

Returns: a new sequence which contains all elements of this sequence followed by all elements of suffix.
Definition Classes: SeqOps -> IterableOps
Inherited from:: SeqOps
Source: Seq.scala

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

Note: may not terminate for infinite-sized collections.

Value parameters

elem: the element to test.

Attributes

Returns: true if this sequence has an element that is equal (as determined by ==) to elem, false otherwise.
Definition Classes: LinearSeqOps -> SeqOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

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

Note: may not terminate for infinite-sized collections.

Value parameters

that: the sequence to test

Attributes

Returns: true if this sequence contains a slice with the same elements as that, otherwise false.
Inherited from:: SeqOps
Source: Seq.scala

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.

Attributes

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

Copies 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.

Attributes

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

Copies 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.

Attributes

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.

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

Attributes

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

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

Attributes

Returns: 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.
Inherited from:: SeqOps
Source: Seq.scala

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.

Attributes

Returns: the number of elements satisfying the predicate p.
Inherited from:: IterableOnceOps
Source: IterableOnce.scala

Computes the multiset difference between this sequence and another sequence.

Value parameters

that: the sequence of elements to remove

Attributes

Returns: a new sequence which contains all elements of this sequence except some of occurrences of elements that also appear in that. If an element value x appears n times in that, then the first n occurrences of x will not form part of the result, but any following occurrences will.
Definition Classes: StrictOptimizedSeqOps -> SeqOps
Inherited from:: StrictOptimizedSeqOps
Source: StrictOptimizedSeqOps.scala

Selects all the elements of this sequence ignoring the duplicates.

Attributes

Returns: a new sequence consisting of all the elements of this sequence without duplicates.
Inherited from:: SeqOps
Source: Seq.scala

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

Attributes

Returns: a new sequence consisting of all the elements of this sequence without duplicates.
Definition Classes: StrictOptimizedSeqOps -> StrictOptimizedSeqOps -> SeqOps
Inherited from:: StrictOptimizedSeqOps
Source: StrictOptimizedSeqOps.scala

Selects all elements except the first n ones.

Value parameters

n: the number of elements to drop from this sequence.

Attributes

Returns: a sequence consisting of all elements of this sequence except the first n ones, or else the empty sequence, if this sequence has less than n elements. If n is negative, don't drop any elements.
Definition Classes: StrictOptimizedLinearSeqOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedLinearSeqOps
Source: LinearSeq.scala

The rest of the collection without its n last elements.

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

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

Attributes

Definition Classes: StrictOptimizedIterableOps -> IterableOps
Inherited from:: StrictOptimizedIterableOps
Source: StrictOptimizedIterableOps.scala

Selects all elements except the longest prefix that satisfies a predicate.

The matching prefix starts with the first element of this sequence, and the element following the prefix is the first element that does not satisfy the predicate. The matching prefix may be empty, so that this method returns the entire sequence.

Example:

scala> List(1, 2, 3, 100, 4).dropWhile(n => n < 10)
val res0: List[Int] = List(100, 4)

scala> List(1, 2, 3, 100, 4).dropWhile(n => n == 0)
val res1: List[Int] = List(1, 2, 3, 100, 4)

Use span to obtain both the prefix and suffix. Use filterNot to drop all elements that satisfy the predicate.

Value parameters

p: The predicate used to test elements.

Attributes

Returns: the longest suffix of this sequence whose first element does not satisfy the predicate p.
Definition Classes: StrictOptimizedLinearSeqOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedLinearSeqOps
Source: LinearSeq.scala

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

Attributes

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

The empty iterable of the same type as this iterable

Attributes

Returns: an empty iterable of type C.
Definition Classes: IterableFactoryDefaults -> IterableOps
Inherited from:: IterableFactoryDefaults
Source: Iterable.scala

Tests whether this sequence ends with the given sequence.

Note: will not terminate for infinite-sized collections.

Value parameters

that: the sequence to test

Attributes

Returns: true if this sequence has that as a suffix, false otherwise.
Inherited from:: SeqOps
Source: Seq.scala

Checks whether this instance is equal to that.

Checks whether this instance is equal to that. This universal equality method is defined in AnyRef.

Attributes

Definition Classes: Seq -> Equals -> Any
Inherited from:: Seq
Source: Seq.scala

Selects all elements of this iterable collection which satisfy a predicate.

Value parameters

p: the predicate used to test elements.

Attributes

Returns: a new iterable collection consisting of all elements of this iterable collection that satisfy the given predicate p. The order of the elements is preserved.
Definition Classes: StrictOptimizedIterableOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedIterableOps
Source: StrictOptimizedIterableOps.scala

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

Value parameters

pred: the predicate used to test elements.

Attributes

Returns: a new iterable collection consisting of all elements of this iterable collection that do not satisfy the given predicate pred. Their order may not be preserved.
Definition Classes: StrictOptimizedIterableOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedIterableOps
Source: StrictOptimizedIterableOps.scala

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

Note: may not terminate for infinite-sized collections.

Value parameters

p: the predicate used to test elements.

Attributes

Returns: an option value containing the first element in the sequence that satisfies p, or None if none exists.
Definition Classes: LinearSeqOps -> IterableOnceOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

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

Note: will not terminate for infinite-sized collections.

Value parameters

p: the predicate used to test elements.

Attributes

Returns: an option value containing the last element in the sequence that satisfies p, or None if none exists.
Definition Classes: LinearSeqOps -> SeqOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

Builds a new iterable collection by applying a function to all elements of this iterable collection 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 iterable collection. 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)

Type parameters

B: the element type of the returned collection.

Value parameters

f: the function to apply to each element.

Attributes

Returns: a new iterable collection resulting from applying the given collection-valued function f to each element of this iterable collection and concatenating the results.
Definition Classes: StrictOptimizedIterableOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedIterableOps
Source: StrictOptimizedIterableOps.scala

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

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

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

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

Type parameters

B: the type of the elements of each iterable collection.

Value parameters

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

Attributes

Returns: a new iterable collection resulting from concatenating all element iterable collections.
Definition Classes: StrictOptimizedIterableOps -> IterableOps -> IterableOnceOps
Inherited from:: StrictOptimizedIterableOps
Source: StrictOptimizedIterableOps.scala

Applies the given binary operator op to the given initial value z and all elements of this collection.

For each application of the operator, each operand is either an element of this collection, the initial value, or another such application of the operator.

The order of applications of the operator is unspecified and may be nondeterministic. Each element appears exactly once in the computation. The initial value may be used an arbitrary number of times, but at least once.

If this collection is ordered, then for any application of the operator, the element(s) appearing in the left operand will precede those in the right.

Note: might return different results for different runs, unless either of the following conditions is met: (1) the operator is associative, and the underlying collection type is ordered; or (2) the operator is associative and commutative. In either case, it is also necessary that the initial value be a neutral value for the operator, e.g. Nil for List concatenation or 1 for multiplication.

The default implementation in IterableOnce is equivalent to foldLeft but may be overridden for more efficient traversal orders.

Note: will not terminate for infinite-sized collections.

Type parameters

A1: The type parameter for the binary operator, a supertype of A.

Value parameters

op: A binary operator; must be associative for the result to always be the same across runs.
z: An initial value; may be used an arbitrary number of times in the computation of the result; must be a neutral value for op for the result to always be the same across runs.

Attributes

Returns: The result of applying op between all the elements and z, or z if this collection is empty.
Inherited from:: IterableOnceOps
Source: IterableOnce.scala

Applies the given binary operator op to the given initial value z and all elements of this sequence, going left to right.

Applies the given binary operator op to the given initial value z and all elements of this sequence, going left to right. Returns the initial value if this sequence is empty.

"Going left to right" only makes sense if this collection is ordered: then if x1, x2, ..., xn are the elements of this sequence, the result is op( op( ... op( op(z, x1), x2) ... ), xn).

If this collection is not ordered, then for each application of the operator, each right operand is an element. In addition, the leftmost operand is the initial value, and each other left operand is itself an application of the operator. The elements of this sequence and the initial value all appear exactly once in the computation.

Note: will not terminate for infinite-sized collections.

Type parameters

B: The result type of the binary operator.

Value parameters

op: A binary operator.
z: An initial value.

Attributes

Returns: The result of applying op to z and all elements of this sequence, going left to right. Returns z if this sequence is empty.
Definition Classes: LinearSeqOps -> IterableOnceOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

Applies the given binary operator op to all elements of this collection and the given initial value z, going right to left.

Applies the given binary operator op to all elements of this collection and the given initial value z, going right to left. Returns the initial value if this collection is empty.

"Going right to left" only makes sense if this collection is ordered: then if x1, x2, ..., xn are the elements of this collection, the result is op(x1, op(x2, op( ... op(xn, z) ... ))).

If this collection is not ordered, then for each application of the operator, each left operand is an element. In addition, the rightmost operand is the initial value, and each other right operand is itself an application of the operator. The elements of this collection and the initial value all appear exactly once in the computation.

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

Note: will not terminate for infinite-sized collections.

Type parameters

B: The result type of the binary operator.

Value parameters

op: A binary operator.
z: An initial value.

Attributes

Returns: The result of applying op to all elements of this collection and z, going right to left. Returns z if this collection is empty.
Inherited from:: IterableOnceOps
Source: IterableOnce.scala

Applies f to each element for its side effects.

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

Attributes

Definition Classes: LinearSeqOps -> IterableOnceOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

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

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

Attributes

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

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

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.

Attributes

Returns

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

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

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

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

Attributes

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.

Attributes

Inherited from:: IterableOps
Source: Iterable.scala

Partitions elements in fixed size iterable collections.

Value parameters

size: the number of elements per group

Attributes

Returns: An iterator producing iterable collections of size size, except the last will be less than size size if the elements don't divide evenly.
See also: scala.collection.Iterator, method grouped
Inherited from:: IterableOps
Source: Iterable.scala

Calculates a hash code value for the object.

The default hashing algorithm is platform dependent.

Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0. However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals method.

Attributes

Returns: the hash code value for this object.
Definition Classes: Seq -> Any
Inherited from:: Seq
Source: Seq.scala

Optionally selects the first element.

Attributes

Returns: the first element of this sequence if it is nonempty, None if it is empty.
Definition Classes: LinearSeqOps -> IterableOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

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

Type parameters

B: the type of the element elem.

Value parameters

elem: the element value to search for.

Attributes

Returns: the index >= 0 of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.
Inherited from:: SeqOps
Source: Seq.scala

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

Type parameters

B: the type of the element elem.

Value parameters

elem: the element value to search for.
from: the start index

Attributes

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

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

Note: may not terminate for infinite-sized collections.

Value parameters

that: the sequence to test

Attributes

Returns: the first index >= 0 such that the elements of this sequence starting at this index match the elements of sequence that, or -1 if no such subsequence exists.
Inherited from:: SeqOps
Source: Seq.scala

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.

Value parameters

from: the start index
that: the sequence to test

Attributes

Returns: the first index >= from such that the elements of this sequence starting at this index match the elements of sequence that, or -1 if no such subsequence exists.
Inherited from:: SeqOps
Source: Seq.scala

Finds index of the first element satisfying some predicate.

Note: may not terminate for infinite-sized collections.

Value parameters

p: the predicate used to test elements.

Attributes

Returns: the index >= 0 of the first element of this sequence that satisfies the predicate p, or -1, if none exists.
Inherited from:: SeqOps
Source: Seq.scala

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

Note: may not terminate for infinite-sized collections.

Value parameters

from: the start index
p: the predicate used to test elements.

Attributes

Returns: the index >= from of the first element of this sequence that satisfies the predicate p, or -1, if none exists.
Definition Classes: LinearSeqOps -> SeqOps
Inherited from:: LinearSeqOps
Source: LinearSeq.scala

Produces the range of all indices of this sequence.

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

Attributes

Returns: a Range value from 0 to one less than the length of this sequence.
Inherited from:: SeqOps
Source