Sequence type that represents lazily evaluated collections. Top-level functions for instantiating sequences and extension functions for sequences.
The sequence operations can be classified into the following groups regarding their state requirements:
If the sequence operation returns another sequence, which is produced lazily, it's called intermediate, and otherwise the operation is terminal. Examples of terminal operations are kotlin.sequences.Sequence.toList, kotlin.sequences.Sequence.max.
Sequences can be iterated multiple times, however some sequence implementations might constrain themselves to be iterated only once. That is mentioned specifically in their documentation (e.g. kotlin.sequences.generateSequence overload). The latter sequences throw an exception on an attempt to iterate them the second time.
interface Sequence<out T> A sequence that returns values through its iterator. The values are evaluated lazily, and the sequence is potentially infinite. |
fun <T> Sequence(iterator: () -> Iterator<T>): Sequence<T> Given an iterator function constructs a Sequence that returns values through the Iterator provided by that function. The values are evaluated lazily, and the sequence is potentially infinite. | |
fun <T> Sequence<T>.all(predicate: (T) -> Boolean): Boolean Returns | |
fun <T> Sequence<T>.any(): Boolean Returns fun <T> Sequence<T>.any(predicate: (T) -> Boolean): Boolean Returns | |
fun <T> Sequence<T>.asIterable(): Iterable<T> Creates an Iterable instance that wraps the original sequence returning its elements when being iterated. | |
fun <T> Sequence<T>.asSequence(): Sequence<T> Returns this sequence as a Sequence. fun <T> Iterator<T>.asSequence(): Sequence<T> Creates a sequence that returns all elements from this iterator. The sequence is constrained to be iterated only once. | |
fun <T, K, V> Sequence<T>.associate( transform: (T) -> Pair<K, V> ): Map<K, V> Returns a Map containing key-value pairs provided by transform function applied to elements of the given sequence. | |
fun <T, K> Sequence<T>.associateBy( keySelector: (T) -> K ): Map<K, T> Returns a Map containing the elements from the given sequence indexed by the key returned from keySelector function applied to each element. fun <T, K, V> Sequence<T>.associateBy( keySelector: (T) -> K, valueTransform: (T) -> V ): Map<K, V> Returns a Map containing the values provided by valueTransform and indexed by keySelector functions applied to elements of the given sequence. | |
fun <T, K, M : MutableMap<in K, in T>> Sequence<T>.associateByTo( destination: M, keySelector: (T) -> K ): M Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function applied to each element of the given sequence and value is the element itself. fun <T, K, V, M : MutableMap<in K, in V>> Sequence<T>.associateByTo( destination: M, keySelector: (T) -> K, valueTransform: (T) -> V ): M Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function and and value is provided by the valueTransform function applied to elements of the given sequence. | |
fun <T, K, V, M : MutableMap<in K, in V>> Sequence<T>.associateTo( destination: M, transform: (T) -> Pair<K, V> ): M Populates and returns the destination mutable map with key-value pairs provided by transform function applied to each element of the given sequence. | |
fun Sequence<Byte>.average(): Double fun Sequence<Short>.average(): Double fun Sequence<Int>.average(): Double fun Sequence<Long>.average(): Double fun Sequence<Float>.average(): Double fun Sequence<Double>.average(): Double Returns an average value of elements in the sequence. | |
fun <T> Sequence<T>.constrainOnce(): Sequence<T> Returns a wrapper sequence that provides values of this sequence, but ensures it can be iterated only one time. | |
operator fun <T> Sequence<T>.contains(element: T): Boolean Returns | |
fun <T> Sequence<T>.count(): Int Returns the number of elements in this sequence. fun <T> Sequence<T>.count(predicate: (T) -> Boolean): Int Returns the number of elements matching the given predicate. | |
fun <T> Sequence<T>.distinct(): Sequence<T> Returns a sequence containing only distinct elements from the given sequence. | |
fun <T, K> Sequence<T>.distinctBy( selector: (T) -> K ): Sequence<T> Returns a sequence containing only elements from the given sequence having distinct keys returned by the given selector function. | |
fun <T> Sequence<T>.drop(n: Int): Sequence<T> Returns a sequence containing all elements except first n elements. | |
fun <T> Sequence<T>.dropWhile( predicate: (T) -> Boolean ): Sequence<T> Returns a sequence containing all elements except first elements that satisfy the given predicate. | |
fun <T> Sequence<T>.elementAt(index: Int): T Returns an element at the given index or throws an IndexOutOfBoundsException if the index is out of bounds of this sequence. | |
fun <T> Sequence<T>.elementAtOrElse( index: Int, defaultValue: (Int) -> T ): T Returns an element at the given index or the result of calling the defaultValue function if the index is out of bounds of this sequence. | |
fun <T> Sequence<T>.elementAtOrNull(index: Int): T? Returns an element at the given index or | |
fun <T> emptySequence(): Sequence<T> Returns an empty sequence. | |
fun <T> Sequence<T>.filter( predicate: (T) -> Boolean ): Sequence<T> Returns a sequence containing only elements matching the given predicate. | |
fun <T> Sequence<T>.filterIndexed( predicate: (index: Int, T) -> Boolean ): Sequence<T> Returns a sequence containing only elements matching the given predicate. | |
fun <T, C : MutableCollection<in T>> Sequence<T>.filterIndexedTo( destination: C, predicate: (index: Int, T) -> Boolean ): C Appends all elements matching the given predicate to the given destination. | |
fun <R> Sequence<*>.filterIsInstance(): Sequence<R> Returns a sequence containing all elements that are instances of specified type parameter R. fun <R> Sequence<*>.filterIsInstance( klass: Class<R> ): Sequence<R> Returns a sequence containing all elements that are instances of specified class. | |
fun <R, C : MutableCollection<in R>> Sequence<*>.filterIsInstanceTo( destination: C ): C Appends all elements that are instances of specified type parameter R to the given destination. fun <C : MutableCollection<in R>, R> Sequence<*>.filterIsInstanceTo( destination: C, klass: Class<R> ): C Appends all elements that are instances of specified class to the given destination. | |
fun <T> Sequence<T>.filterNot( predicate: (T) -> Boolean ): Sequence<T> Returns a sequence containing all elements not matching the given predicate. | |
fun <T : Any> Sequence<T?>.filterNotNull(): Sequence<T> Returns a sequence containing all elements that are not | |
fun <C : MutableCollection<in T>, T : Any> Sequence<T?>.filterNotNullTo( destination: C ): C Appends all elements that are not | |
fun <T, C : MutableCollection<in T>> Sequence<T>.filterNotTo( destination: C, predicate: (T) -> Boolean ): C Appends all elements not matching the given predicate to the given destination. | |
fun <T, C : MutableCollection<in T>> Sequence<T>.filterTo( destination: C, predicate: (T) -> Boolean ): C Appends all elements matching the given predicate to the given destination. | |
fun <T> Sequence<T>.find(predicate: (T) -> Boolean): T? Returns the first element matching the given predicate, or | |
fun <T> Sequence<T>.findLast(predicate: (T) -> Boolean): T? Returns the last element matching the given predicate, or | |
fun <T> Sequence<T>.first(): T Returns first element. fun <T> Sequence<T>.first(predicate: (T) -> Boolean): T Returns the first element matching the given predicate. | |
fun <T> Sequence<T>.firstOrNull(): T? Returns the first element, or fun <T> Sequence<T>.firstOrNull( predicate: (T) -> Boolean ): T? Returns the first element matching the given predicate, or | |
fun <T, R> Sequence<T>.flatMap( transform: (T) -> Sequence<R> ): Sequence<R> Returns a single sequence of all elements from results of transform function being invoked on each element of original sequence. | |
fun <T, R, C : MutableCollection<in R>> Sequence<T>.flatMapTo( destination: C, transform: (T) -> Sequence<R> ): C Appends all elements yielded from results of transform function being invoked on each element of original sequence, to the given destination. | |
fun <T> Sequence<Sequence<T>>.flatten(): Sequence<T> Returns a sequence of all elements from all sequences in this sequence. fun <T> Sequence<Iterable<T>>.flatten(): Sequence<T> Returns a sequence of all elements from all iterables in this sequence. | |
fun <T, R> Sequence<T>.fold( initial: R, operation: (acc: R, T) -> R ): R Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each element. | |
fun <T, R> Sequence<T>.foldIndexed( initial: R, operation: (index: Int, acc: R, T) -> R ): R Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each element with its index in the original sequence. | |
fun <T> Sequence<T>.forEach(action: (T) -> Unit) Performs the given action on each element. | |
fun <T> Sequence<T>.forEachIndexed( action: (index: Int, T) -> Unit) Performs the given action on each element, providing sequential index with the element. | |
fun <T : Any> generateSequence( nextFunction: () -> T? ): Sequence<T> Returns a sequence which invokes the function to calculate the next value on each iteration until the function returns fun <T : Any> generateSequence( seed: T?, nextFunction: (T) -> T? ): Sequence<T> Returns a sequence defined by the starting value seed and the function nextFunction, which is invoked to calculate the next value based on the previous one on each iteration. fun <T : Any> generateSequence( seedFunction: () -> T?, nextFunction: (T) -> T? ): Sequence<T> Returns a sequence defined by the function seedFunction, which is invoked to produce the starting value, and the nextFunction, which is invoked to calculate the next value based on the previous one on each iteration. | |
fun <T, K> Sequence<T>.groupBy( keySelector: (T) -> K ): Map<K, List<T>> Groups elements of the original sequence by the key returned by the given keySelector function applied to each element and returns a map where each group key is associated with a list of corresponding elements. fun <T, K, V> Sequence<T>.groupBy( keySelector: (T) -> K, valueTransform: (T) -> V ): Map<K, List<V>> Groups values returned by the valueTransform function applied to each element of the original sequence by the key returned by the given keySelector function applied to the element and returns a map where each group key is associated with a list of corresponding values. | |
fun <T, K, M : MutableMap<in K, MutableList<T>>> Sequence<T>.groupByTo( destination: M, keySelector: (T) -> K ): M Groups elements of the original sequence by the key returned by the given keySelector function applied to each element and puts to the destination map each group key associated with a list of corresponding elements. fun <T, K, V, M : MutableMap<in K, MutableList<V>>> Sequence<T>.groupByTo( destination: M, keySelector: (T) -> K, valueTransform: (T) -> V ): M Groups values returned by the valueTransform function applied to each element of the original sequence by the key returned by the given keySelector function applied to the element and puts to the destination map each group key associated with a list of corresponding values. | |
fun <T, K> Sequence<T>.groupingBy( keySelector: (T) -> K ): Grouping<T, K> Creates a Grouping source from a sequence to be used later with one of group-and-fold operations using the specified keySelector function to extract a key from each element. | |
fun <T> Sequence<T>.indexOf(element: T): Int Returns first index of element, or -1 if the sequence does not contain element. | |
fun <T> Sequence<T>.indexOfFirst( predicate: (T) -> Boolean ): Int Returns index of the first element matching the given predicate, or -1 if the sequence does not contain such element. | |
fun <T> Sequence<T>.indexOfLast( predicate: (T) -> Boolean ): Int Returns index of the last element matching the given predicate, or -1 if the sequence does not contain such element. | |
fun <T, A> Sequence<T>.joinTo( buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: (T) -> CharSequence = null ): A Appends the string from all the elements separated using separator and using the given prefix and postfix if supplied. | |
fun <T> Sequence<T>.joinToString( separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: (T) -> CharSequence = null ): String Creates a string from all the elements separated using separator and using the given prefix and postfix if supplied. | |
fun <T> Sequence<T>.last(): T Returns the last element. fun <T> Sequence<T>.last(predicate: (T) -> Boolean): T Returns the last element matching the given predicate. | |
fun <T> Sequence<T>.lastIndexOf(element: T): Int Returns last index of element, or -1 if the sequence does not contain element. | |
fun <T> Sequence<T>.lastOrNull(): T? Returns the last element, or fun <T> Sequence<T>.lastOrNull(predicate: (T) -> Boolean): T? Returns the last element matching the given predicate, or | |
fun <T, R> Sequence<T>.map(transform: (T) -> R): Sequence<R> Returns a sequence containing the results of applying the given transform function to each element in the original sequence. | |
fun <T, R> Sequence<T>.mapIndexed( transform: (index: Int, T) -> R ): Sequence<R> Returns a sequence containing the results of applying the given transform function to each element and its index in the original sequence. | |
fun <T, R : Any> Sequence<T>.mapIndexedNotNull( transform: (index: Int, T) -> R? ): Sequence<R> Returns a sequence containing only the non-null results of applying the given transform function to each element and its index in the original sequence. | |
fun <T, R : Any, C : MutableCollection<in R>> Sequence<T>.mapIndexedNotNullTo( destination: C, transform: (index: Int, T) -> R? ): C Applies the given transform function to each element and its index in the original sequence and appends only the non-null results to the given destination. | |
fun <T, R, C : MutableCollection<in R>> Sequence<T>.mapIndexedTo( destination: C, transform: (index: Int, T) -> R ): C Applies the given transform function to each element and its index in the original sequence and appends the results to the given destination. | |
fun <T, R : Any> Sequence<T>.mapNotNull( transform: (T) -> R? ): Sequence<R> Returns a sequence containing only the non-null results of applying the given transform function to each element in the original sequence. | |
fun <T, R : Any, C : MutableCollection<in R>> Sequence<T>.mapNotNullTo( destination: C, transform: (T) -> R? ): C Applies the given transform function to each element in the original sequence and appends only the non-null results to the given destination. | |
fun <T, R, C : MutableCollection<in R>> Sequence<T>.mapTo( destination: C, transform: (T) -> R ): C Applies the given transform function to each element of the original sequence and appends the results to the given destination. | |
fun Sequence<Double>.max(): Double? fun Sequence<Float>.max(): Float? fun <T : Comparable<T>> Sequence<T>.max(): T? Returns the largest element or | |
fun <T, R : Comparable<R>> Sequence<T>.maxBy( selector: (T) -> R ): T? Returns the first element yielding the largest value of the given function or | |
fun <T> Sequence<T>.maxWith(comparator: Comparator<in T>): T? fun <T> Sequence<T>.maxWith(comparator: Comparator<in T>): T? Returns the first element having the largest value according to the provided comparator or | |
fun Sequence<Double>.min(): Double? fun Sequence<Float>.min(): Float? fun <T : Comparable<T>> Sequence<T>.min(): T? Returns the smallest element or | |
fun <T, R : Comparable<R>> Sequence<T>.minBy( selector: (T) -> R ): T? Returns the first element yielding the smallest value of the given function or | |
fun <T> Sequence<T>.minWith(comparator: Comparator<in T>): T? fun <T> Sequence<T>.minWith(comparator: Comparator<in T>): T? Returns the first element having the smallest value according to the provided comparator or | |
operator fun <T> Sequence<T>.minus(element: T): Sequence<T> Returns a sequence containing all elements of the original sequence without the first occurrence of the given element. operator fun <T> Sequence<T>.minus( elements: Array<out T> ): Sequence<T> Returns a sequence containing all elements of original sequence except the elements contained in the given elements array. operator fun <T> Sequence<T>.minus( elements: Iterable<T> ): Sequence<T> Returns a sequence containing all elements of original sequence except the elements contained in the given elements collection. operator fun <T> Sequence<T>.minus( elements: Sequence<T> ): Sequence<T> Returns a sequence containing all elements of original sequence except the elements contained in the given elements sequence. | |
fun <T> Sequence<T>.minusElement(element: T): Sequence<T> Returns a sequence containing all elements of the original sequence without the first occurrence of the given element. | |
fun <T> Sequence<T>.none(): Boolean Returns fun <T> Sequence<T>.none(predicate: (T) -> Boolean): Boolean Returns | |
fun <T> Sequence<T>.onEach(action: (T) -> Unit): Sequence<T> Returns a sequence which performs the given action on each element of the original sequence as they pass though it. | |
fun <T> Sequence<T>.partition( predicate: (T) -> Boolean ): Pair<List<T>, List<T>> Splits the original sequence into pair of lists, where first list contains elements for which predicate yielded | |
operator fun <T> Sequence<T>.plus(element: T): Sequence<T> Returns a sequence containing all elements of the original sequence and then the given element. operator fun <T> Sequence<T>.plus( elements: Array<out T> ): Sequence<T> Returns a sequence containing all elements of original sequence and then all elements of the given elements array. operator fun <T> Sequence<T>.plus( elements: Iterable<T> ): Sequence<T> Returns a sequence containing all elements of original sequence and then all elements of the given elements collection. operator fun <T> Sequence<T>.plus( elements: Sequence<T> ): Sequence<T> Returns a sequence containing all elements of original sequence and then all elements of the given elements sequence. | |
fun <T> Sequence<T>.plusElement(element: T): Sequence<T> Returns a sequence containing all elements of the original sequence and then the given element. | |
fun <S, T : S> Sequence<T>.reduce( operation: (acc: S, T) -> S ): S Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element. | |
fun <S, T : S> Sequence<T>.reduceIndexed( operation: (index: Int, acc: S, T) -> S ): S Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original sequence. | |
fun <T : Any> Sequence<T?>.requireNoNulls(): Sequence<T> Returns an original collection containing all the non- | |
fun <T> sequenceOf(vararg elements: T): Sequence<T> Creates a sequence that returns the specified values. | |
fun <T> Sequence<T>.single(): T Returns the single element, or throws an exception if the sequence is empty or has more than one element. fun <T> Sequence<T>.single(predicate: (T) -> Boolean): T Returns the single element matching the given predicate, or throws exception if there is no or more than one matching element. | |
fun <T> Sequence<T>.singleOrNull(): T? Returns single element, or fun <T> Sequence<T>.singleOrNull( predicate: (T) -> Boolean ): T? Returns the single element matching the given predicate, or | |
fun <T : Comparable<T>> Sequence<T>.sorted(): Sequence<T> Returns a sequence that yields elements of this sequence sorted according to their natural sort order. | |
fun <T, R : Comparable<R>> Sequence<T>.sortedBy( selector: (T) -> R? ): Sequence<T> Returns a sequence that yields elements of this sequence sorted according to natural sort order of the value returned by specified selector function. | |
fun <T, R : Comparable<R>> Sequence<T>.sortedByDescending( selector: (T) -> R? ): Sequence<T> Returns a sequence that yields elements of this sequence sorted descending according to natural sort order of the value returned by specified selector function. | |
fun <T : Comparable<T>> Sequence<T>.sortedDescending(): Sequence<T> Returns a sequence that yields elements of this sequence sorted descending according to their natural sort order. | |
fun <T> Sequence<T>.sortedWith( comparator: Comparator<in T> ): Sequence<T> fun <T> Sequence<T>.sortedWith( comparator: Comparator<in T> ): Sequence<T> Returns a sequence that yields elements of this sequence sorted according to the specified comparator. | |
fun Sequence<Byte>.sum(): Int fun Sequence<Short>.sum(): Int fun Sequence<Int>.sum(): Int fun Sequence<Long>.sum(): Long fun Sequence<Float>.sum(): Float fun Sequence<Double>.sum(): Double Returns the sum of all elements in the sequence. | |
fun <T> Sequence<T>.sumBy(selector: (T) -> Int): Int Returns the sum of all values produced by selector function applied to each element in the sequence. | |
fun <T> Sequence<T>.sumByDouble( selector: (T) -> Double ): Double Returns the sum of all values produced by selector function applied to each element in the sequence. | |
fun <T> Sequence<T>.take(n: Int): Sequence<T> Returns a sequence containing first n elements. | |
fun <T> Sequence<T>.takeWhile( predicate: (T) -> Boolean ): Sequence<T> Returns a sequence containing first elements satisfying the given predicate. | |
fun <T, C : MutableCollection<in T>> Sequence<T>.toCollection( destination: C ): C Appends all elements to the given destination collection. | |
fun <T> Sequence<T>.toHashSet(): HashSet<T> Returns a HashSet of all elements. | |
fun <T> Sequence<T>.toList(): List<T> Returns a List containing all elements. | |
fun <T> Sequence<T>.toMutableList(): MutableList<T> Returns a MutableList filled with all elements of this sequence. | |
fun <T> Sequence<T>.toMutableSet(): MutableSet<T> Returns a mutable set containing all distinct elements from the given sequence. | |
fun <T> Sequence<T>.toSet(): Set<T> Returns a Set of all elements. | |
fun <T : Comparable<T>> Sequence<T>.toSortedSet(): SortedSet<T> fun <T> Sequence<T>.toSortedSet( comparator: Comparator<in T> ): SortedSet<T> Returns a SortedSet of all elements. | |
fun <T, R> Sequence<Pair<T, R>>.unzip(): Pair<List<T>, List<R>> Returns a pair of lists, where first list is built from the first values of each pair from this sequence, second list is built from the second values of each pair from this sequence. | |
fun <T> Sequence<T>.withIndex(): Sequence<IndexedValue<T>> Returns a sequence of IndexedValue for each element of the original sequence. | |
infix fun <T, R> Sequence<T>.zip( other: Sequence<R> ): Sequence<Pair<T, R>> Returns a sequence of pairs built from elements of both sequences with same indexes. Resulting sequence has length of shortest input sequence. fun <T, R, V> Sequence<T>.zip( other: Sequence<R>, transform: (a: T, b: R) -> V ): Sequence<V> Returns a sequence of values built from elements of both collections with same indexes using provided transform. Resulting sequence has length of shortest input sequences. |
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https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.sequences/