kotlin-stdlib/kotlin.collections/reduceIndexedOrNull

reduceIndexedOrNull

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

Returns null if the array is empty.

Since Kotlin

1.4

Samples

import samples.*
import kotlin.test.*
fun main() { 
   //sampleStart 
   val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceOrNull { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }, "ab1c2d3")

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

Parameters

operation

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


inline fun <S, T : S> Iterable<T>.reduceIndexedOrNull(operation: (index: Int, S, T) -> S): S?
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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.

Returns null if the collection is empty.

Since Kotlin

1.4

Samples

import samples.*
import kotlin.test.*
fun main() { 
   //sampleStart 
   val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceOrNull { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }, "ab1c2d3")

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

Parameters

operation

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