Kotlin List reduceRightOrNull()
Syntax & Examples

Syntax of List.reduceRightOrNull()

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

fun <S, T : S> List<T>.reduceRightOrNull( operation: (T, acc: S) -> S ): S?

This reduceRightOrNull() extension function of List accumulates value starting with the last element and applying operation from right to left to each element and current accumulator 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 reduceRightOrNull function to accumulate the elements from right to left by adding each element to the accumulator.
The final accumulated value, which is an integer sum, 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.reduceRightOrNull { element, acc -> element + acc }
    println(result)
}

Output

2 Example

In this example,

We create a list of strings named list containing elements "apple", "banana", "cherry", "date", "elderberry".
We use the reduceRightOrNull function to accumulate the strings from right to left by concatenating them with the accumulator with spaces.
The final accumulated value, which is a string concatenation with spaces, is stored in result.
We print result using println().

Kotlin Program

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

Output

apple banana cherry date elderberry

Summary

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