runningFold
Returns a sequence containing successive accumulation values generated by applying operation from left to right to each element and current accumulator value that starts with initial value.
Note that
acc
value passed to
operation
function should not be mutated;
otherwise it would affect the previous value in resulting sequence.
The
initial
value should also be immutable (or should not be mutated)
as it may be passed to
operation
function later because of sequence's lazy nature.
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.runningFold("s") { acc, string -> acc + string }) // [s, sa, sab, sabc, sabcd]
println(strings.runningFoldIndexed("s") { index, acc, string -> acc + string + index }) // [s, sa0, sa0b1, sa0b1c2, sa0b1c2d3]
println(emptyList<String>().runningFold("s") { _, _ -> "X" }) // [s]
//sampleEnd
}
Parameters
function that takes current accumulator value and an element, and calculates the next accumulator value.
The operation is intermediate and stateless .