reduceRightIndexedOrNull (original) (raw)

Accumulates value starting with the last element and applying operation from right to left to each element with its index in the original array and current accumulator value.

Returns null if the array is empty.

Since Kotlin

1.4

Parameters

operation

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

Samples

import kotlin.math.*
import kotlin.test.*

fun main() { 
   //sampleStart 
   val strings = listOf("a", "b", "c", "d")
println(strings.reduceRightOrNull { string, acc -> acc + string }) // dcba
println(strings.reduceRightIndexedOrNull { index, string, acc -> acc + string + index }) // dc2b1a0

println(emptyList<String>().reduceRightOrNull { _, _ -> "" }) // null 
   //sampleEnd
}

Accumulates value starting with the last element and applying operation from right to left to each element with its index in the original list and current accumulator value.

Returns null if the list is empty.

Since Kotlin

1.4

Parameters

operation

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

Samples

import kotlin.math.*
import kotlin.test.*

fun main() { 
   //sampleStart 
   val strings = listOf("a", "b", "c", "d")
println(strings.reduceRightOrNull { string, acc -> acc + string }) // dcba
println(strings.reduceRightIndexedOrNull { index, string, acc -> acc + string + index }) // dc2b1a0

println(emptyList<String>().reduceRightOrNull { _, _ -> "" }) // null 
   //sampleEnd
}