reduce
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.
Throws an exception if this array is empty. If the array can be empty in an expected way, please use reduceIndexedOrNull 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.reduce { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexed { index, acc, string -> acc + string + index }, "ab1c2d3")
assertFails { emptyList<Int>().reduce { _, _ -> 0 } }
//sampleEnd
}Parameters
function that takes the index of an element, current accumulator value and the element itself, and calculates the next accumulator value.
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.
Throws an exception if this collection is empty. If the collection can be empty in an expected way, please use reduceIndexedOrNull 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.reduce { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexed { index, acc, string -> acc + string + index }, "ab1c2d3")
assertFails { emptyList<Int>().reduce { _, _ -> 0 } }
//sampleEnd
}Parameters
function that takes the index of an element, current accumulator value and the element itself, and calculates the next accumulator value.
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.
Throws an exception if this array is empty. If the array can be empty in an expected way, please use reduceIndexedOrNull 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.reduce { acc, string -> acc + string }, "abcd")
assertPrints(strings.reduceIndexed { index, acc, string -> acc + string + index }, "ab1c2d3")
assertFails { emptyList<Int>().reduce { _, _ -> 0 } }
//sampleEnd
}Parameters
function that takes the index of an element, current accumulator value and the element itself, and calculates the next accumulator value.