kotlin-stdlib/kotlin.collections/reduceRightIndexed

reduceRightIndexed

inline fun <S, T : S> Array<out T>.reduceRightIndexed(operation: (index: Int, T, acc: S) -> S): S(source)
inline fun ByteArray.reduceRightIndexed(operation: (index: Int, Byte, acc: Byte) -> Byte): Byte(source)
inline fun ShortArray.reduceRightIndexed(operation: (index: Int, Short, acc: Short) -> Short): Short(source)
inline fun IntArray.reduceRightIndexed(operation: (index: Int, Int, acc: Int) -> Int): Int(source)
inline fun LongArray.reduceRightIndexed(operation: (index: Int, Long, acc: Long) -> Long): Long(source)
inline fun FloatArray.reduceRightIndexed(operation: (index: Int, Float, acc: Float) -> Float): Float(source)
inline fun DoubleArray.reduceRightIndexed(operation: (index: Int, Double, acc: Double) -> Double): Double(source)
inline fun BooleanArray.reduceRightIndexed(operation: (index: Int, Boolean, acc: Boolean) -> Boolean): Boolean(source)
inline fun CharArray.reduceRightIndexed(operation: (index: Int, Char, acc: Char) -> Char): Char(source)

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.

Throws an exception if this array is empty. If the array can be empty in an expected way, please use reduceRightIndexedOrNull instead. It returns null when its receiver is empty.

Since Kotlin

1.0

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.test.*

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

// emptyList<Int>().reduceRight { _, _ -> 0 } // will fail 
   //sampleEnd
}
inline fun <S, T : S> List<T>.reduceRightIndexed(operation: (index: Int, T, acc: S) -> S): S(source)

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.

Throws an exception if this list is empty. If the list can be empty in an expected way, please use reduceRightIndexedOrNull instead. It returns null when its receiver is empty.

Since Kotlin

1.0

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.test.*

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

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