reduce
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.
Samples
import samples.*
import kotlin.test.*
fun main() {
//sampleStart
val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceRight { string, acc -> acc + string }, "dcba")
assertPrints(strings.reduceRightIndexed { index, string, acc -> acc + string + index }, "dc2b1a0")
assertFails { emptyList<Int>().reduceRight { _, _ -> 0 } }
//sampleEnd
}Parameters
function that takes the index of an element, the element itself and current accumulator value, and calculates the next accumulator value.
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.
Samples
import samples.*
import kotlin.test.*
fun main() {
//sampleStart
val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceRight { string, acc -> acc + string }, "dcba")
assertPrints(strings.reduceRightIndexed { index, string, acc -> acc + string + index }, "dc2b1a0")
assertFails { emptyList<Int>().reduceRight { _, _ -> 0 } }
//sampleEnd
}Parameters
function that takes the index of an element, the element itself and current accumulator value, and calculates the next accumulator value.
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
Samples
import samples.*
import kotlin.test.*
fun main() {
//sampleStart
val strings = listOf("a", "b", "c", "d")
assertPrints(strings.reduceRight { string, acc -> acc + string }, "dcba")
assertPrints(strings.reduceRightIndexed { index, string, acc -> acc + string + index }, "dc2b1a0")
assertFails { emptyList<Int>().reduceRight { _, _ -> 0 } }
//sampleEnd
}Parameters
function that takes the index of an element, the element itself and current accumulator value, and calculates the next accumulator value.