Kotlin List runningFold()
Syntax & Examples

Syntax of List.runningFold()

The syntax of List.runningFold() extension function is:

fun <T, R> Iterable<T>.runningFold( initial: R, operation: (acc: R, T) -> R ): List<R>

This runningFold() extension function of List returns a list containing successive accumulation values generated by applying operation from left to right to each element and current accumulator value that starts with initial value.

✐ Examples

1 Example

In this example,

We create a list of integers named list containing elements 1, 2, 3, 4, 5.
We use the runningFold function to apply addition from left to right starting with an initial value of 0.
The resulting list of accumulated values is stored in result.
We print result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(1, 2, 3, 4, 5)
    val result = list.runningFold(0) { acc, element -> acc + element }
    println(result)
}

Output

[0, 1, 3, 6, 10, 15]

2 Example

In this example,

We create a list of strings named list containing elements "apple", "banana", "cherry".
We use the runningFold function to concatenate strings from left to right starting with an empty string ''.
The resulting list of accumulated strings is stored in result.
We print result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf("apple", "banana", "cherry")
    val result = list.runningFold("") { acc, element -> acc + element }
    println(result)
}

Output

[, apple, applebanana, applebananacherry]

Summary

In this Kotlin tutorial, we learned about runningFold() extension function of List: the syntax and few working examples with output and detailed explanation for each example.