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.