kotlin-stdlib/kotlin.collections/Grouping

Grouping

interface Grouping<T, out K>(source)

Represents a source of elements with a keyOf function, which can be applied to each element to get its key.

A Grouping structure serves as an intermediate step in group-and-fold operations: they group elements by their keys and then fold each group with some aggregating operation.

It is created by attaching keySelector: (T) -> K function to a source of elements. To get an instance of Grouping use one of groupingBy extension functions:

For the list of group-and-fold operations available, see the #extension-functions for Grouping.

Since Kotlin

1.1

Functions

inline fun <T, K, R> Grouping<T, K>.aggregate(operation: (key: K, accumulator: R?, element: T, first: Boolean) -> R): Map<K, R>

Groups elements from the Grouping source by key and applies operation to the elements of each group sequentially, passing the previously accumulated value and the current element as arguments, and stores the results in a new map.

Since Kotlin 1.1

inline fun <T, K, R, M : MutableMap<in K, R>> Grouping<T, K>.aggregateTo(destination: M, operation: (key: K, accumulator: R?, element: T, first: Boolean) -> R): M

Groups elements from the Grouping source by key and applies operation to the elements of each group sequentially, passing the previously accumulated value and the current element as arguments, and stores the results in the given destination map.

Since Kotlin 1.1

expect fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>

Since Kotlin 1.0

actual fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>

Groups elements from the Grouping source by key and counts elements in each group.

Since Kotlin 1.1

actual fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>

Groups elements from the Grouping source by key and counts elements in each group.

Since Kotlin 1.1

actual fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>

Groups elements from the Grouping source by key and counts elements in each group.

Since Kotlin 1.3

actual fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>

Groups elements from the Grouping source by key and counts elements in each group.

Since Kotlin 1.8

actual fun <T, K> Grouping<T, K>.eachCount(): Map<K, Int>

Groups elements from the Grouping source by key and counts elements in each group.

Since Kotlin 1.8

fun <T, K, M : MutableMap<in K, Int>> Grouping<T, K>.eachCountTo(destination: M): M

Groups elements from the Grouping source by key and counts elements in each group to the given destination map.

Since Kotlin 1.1

inline fun <T, K, R> Grouping<T, K>.fold(initialValue: R, operation: (accumulator: R, element: T) -> R): Map<K, R>

Groups elements from the Grouping source by key and applies operation to the elements of each group sequentially, passing the previously accumulated value and the current element as arguments, and stores the results in a new map. An initial value of accumulator is the same initialValue for each group.

Since Kotlin 1.1

inline fun <T, K, R> Grouping<T, K>.fold(initialValueSelector: (key: K, element: T) -> R, operation: (key: K, accumulator: R, element: T) -> R): Map<K, R>

Groups elements from the Grouping source by key and applies operation to the elements of each group sequentially, passing the previously accumulated value and the current element as arguments, and stores the results in a new map. An initial value of accumulator is provided by initialValueSelector function.

Since Kotlin 1.1

inline fun <T, K, R, M : MutableMap<in K, R>> Grouping<T, K>.foldTo(destination: M, initialValue: R, operation: (accumulator: R, element: T) -> R): M

Groups elements from the Grouping source by key and applies operation to the elements of each group sequentially, passing the previously accumulated value and the current element as arguments, and stores the results in the given destination map. An initial value of accumulator is the same initialValue for each group.

Since Kotlin 1.1

inline fun <T, K, R, M : MutableMap<in K, R>> Grouping<T, K>.foldTo(destination: M, initialValueSelector: (key: K, element: T) -> R, operation: (key: K, accumulator: R, element: T) -> R): M

Groups elements from the Grouping source by key and applies operation to the elements of each group sequentially, passing the previously accumulated value and the current element as arguments, and stores the results in the given destination map. An initial value of accumulator is provided by initialValueSelector function.

Since Kotlin 1.1

abstract fun keyOf(element: T): K

Extracts the key of an element.

Since Kotlin 1.1

inline fun <S, T : S, K> Grouping<T, K>.reduce(operation: (key: K, accumulator: S, element: T) -> S): Map<K, S>

Groups elements from the Grouping source by key and applies the reducing operation to the elements of each group sequentially starting from the second element of the group, passing the previously accumulated value and the current element as arguments, and stores the results in a new map. An initial value of accumulator is the first element of the group.

Since Kotlin 1.1

inline fun <S, T : S, K, M : MutableMap<in K, S>> Grouping<T, K>.reduceTo(destination: M, operation: (key: K, accumulator: S, element: T) -> S): M

Groups elements from the Grouping source by key and applies the reducing operation to the elements of each group sequentially starting from the second element of the group, passing the previously accumulated value and the current element as arguments, and stores the results in the given destination map. An initial value of accumulator is the first element of the group.

Since Kotlin 1.1

abstract fun sourceIterator(): Iterator<T>

Returns an Iterator over the elements of the source of this grouping.

Since Kotlin 1.1

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