How to Find Sum of List in Kotlin: Simple Guide

To find the sum of a list in Kotlin, use the sum() function directly on the list of numbers. For example, val total = listOf(1, 2, 3).sum() calculates the sum of the list elements.

Syntax

The sum() function is called on a list of numbers to get their total sum.

• listOf(...): Creates a list of numbers.
• .sum(): Adds all numbers in the list and returns the total.
• val total: Stores the sum result.

kotlin

val total = listOf(1, 2, 3, 4, 5).sum()

Example

This example shows how to create a list of integers and find their sum using sum(). It prints the total sum to the console.

kotlin

fun main() {
    val numbers = listOf(10, 20, 30, 40)
    val total = numbers.sum()
    println("Sum of the list is: $total")
}

Output

Sum of the list is: 100

Common Pitfalls

One common mistake is trying to use sum() on a list of non-numeric types like strings, which will cause an error. Also, using sum() on an empty list returns 0, which is expected but good to remember.

For lists of other numeric types like Double or Float, use sum() as well, but ensure the list type matches.

kotlin

/* Wrong: sum() on list of strings causes error */
// val words = listOf("a", "b", "c")
// val total = words.sum() // Error: Unresolved reference

/* Right: sum() on list of integers */
val numbers = listOf(1, 2, 3)
val total = numbers.sum()

Quick Reference

Function	Description
sum()	Returns the sum of all elements in a numeric list.
sumBy(selector)	Sums values returned by selector function (deprecated, use sumOf).
sumOf(selector)	Sums values returned by selector function, supports transformations.

Key Takeaways

Use the built-in sum() function to get the total of a numeric list in Kotlin.

Ensure the list contains numeric types like Int, Double, or Float before calling sum().

Calling sum() on an empty list returns 0 without errors.

For custom calculations, use sumOf() with a selector function.

Avoid using sum() on non-numeric lists to prevent errors.