Kotlin List sumOf()
Syntax & Examples

Syntax of List.sumOf()

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

fun <T> Iterable<T>.sumOf(selector: (T) -> Double): Double

This sumOf() extension function of List returns the sum of all values produced by selector function applied to each element in the collection.

✐ Examples

1 Example

In this example,

We create a list of doubles named list1 with elements 1.5, 2.7, 3.9, 4.1.
We apply the sumOf function on list1 using a selector that doubles each element.
The result is the sum of all doubled elements, which is 24.4.
We print the result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1.5, 2.7, 3.9, 4.1)
    val result = list1.sumOf { it * 2 }
    println(result)
}

Output

24.4

2 Example

In this example,

We create a list of characters named list1 with elements 'a', 'b', 'c', 'd'.
We convert each character to its ASCII value as double using toInt().toDouble() in the selector function.
We apply the sumOf function on list1 using this selector.
The result is the sum of ASCII values of characters, which is 394.0.
We print the result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf('a', 'b', 'c', 'd')
    val result = list1.sumOf { it.toInt().toDouble() }
    println(result)
}

Output

394.0

3 Example

In this example,

We create a list of strings named list1 with elements "apple", "banana", "cherry", "date".
We apply the sumOf function on list1 using a selector that calculates the length of each string as a double.
The result is the sum of lengths of all strings, which is 21.0.
We print the result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry", "date")
    val result = list1.sumOf { it.length.toDouble() }
    println(result)
}

Output

21.0

Summary

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