kotlin-stdlib / kotlin.collections / reduceIndexed

reduceIndexed

Common
JVM
JS
Native
1.0
inline fun <S, T : S> Array<out T>.reduceIndexed(
    operation: (index: Int, acc: S, T) -> S
): S
inline fun ByteArray.reduceIndexed(
    operation: (index: Int, acc: Byte, Byte) -> Byte
): Byte
inline fun ShortArray.reduceIndexed(
    operation: (index: Int, acc: Short, Short) -> Short
): Short
inline fun IntArray.reduceIndexed(
    operation: (index: Int, acc: Int, Int) -> Int
): Int
inline fun LongArray.reduceIndexed(
    operation: (index: Int, acc: Long, Long) -> Long
): Long
inline fun FloatArray.reduceIndexed(
    operation: (index: Int, acc: Float, Float) -> Float
): Float
inline fun DoubleArray.reduceIndexed(
    operation: (index: Int, acc: Double, Double) -> Double
): Double
inline fun BooleanArray.reduceIndexed(
    operation: (index: Int, acc: Boolean, Boolean) -> Boolean
): Boolean
inline fun CharArray.reduceIndexed(
    operation: (index: Int, acc: Char, Char) -> Char
): Char
@ExperimentalUnsignedTypes inline fun UIntArray.reduceIndexed(
    operation: (index: Int, acc: UInt, UInt) -> UInt
): UInt
@ExperimentalUnsignedTypes inline fun ULongArray.reduceIndexed(
    operation: (index: Int, acc: ULong, ULong) -> ULong
): ULong
@ExperimentalUnsignedTypes inline fun UByteArray.reduceIndexed(
    operation: (index: Int, acc: UByte, UByte) -> UByte
): UByte
@ExperimentalUnsignedTypes inline fun UShortArray.reduceIndexed(
    operation: (index: Int, acc: UShort, UShort) -> UShort
): UShort

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 array.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduce { acc, string -> acc + string }) // abcd
println(strings.reduceIndexed { index, acc, string -> acc + string + index }) // ab1c2d3

// emptyList<Int>().reduce { _, _ -> 0 } //  will fail
//sampleEnd
}

Parameters

operation - function that takes the index of an element, current accumulator value and the element itself and calculates the next accumulator value.

Common
JVM
JS
Native
1.0
inline fun <S, T : S> Iterable<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 collection.

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduce { acc, string -> acc + string }) // abcd
println(strings.reduceIndexed { index, acc, string -> acc + string + index }) // ab1c2d3

// emptyList<Int>().reduce { _, _ -> 0 } //  will fail
//sampleEnd
}

Parameters

operation - function that takes the index of an element, current accumulator value and the element itself and calculates the next accumulator value.