Kotlin List filter()
Syntax & Examples

Syntax of List.filter()

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

fun <T> Iterable<T>.filter( predicate: (T) -> Boolean ): List<T>

This filter() extension function of List returns a list containing only elements matching the given predicate.

✐ Examples

1 Example

In this example,

We create a list named list containing the integers 1, 2, 3, 4, 5.
We apply the filter extension function on list to filter out only the even numbers using the predicate { it % 2 == 0 }.
The filtered elements are stored in the result list.
Finally, we print the result list to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(1, 2, 3, 4, 5);
    val result = list.filter { it % 2 == 0 };
    println(result);
}

Output

[2, 4]

2 Example

In this example,

We create a list named list containing the characters 'a', 'b', 'c', 'd', 'e'.
We apply the filter extension function on list to filter out only the characters 'a' and 'e' using the predicate { it in listOf('a', 'e') }.
The filtered elements are stored in the result list.
Finally, we print the result list to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf('a', 'b', 'c', 'd', 'e');
    val result = list.filter { it in listOf('a', 'e') };
    println(result);
}

Output

[a, e]

3 Example

In this example,

We create a list named list containing the strings "apple", "banana", "orange", "grape".
We apply the filter extension function on list to filter out only the strings with length greater than 5 using the predicate { it.length > 5 }.
The filtered elements are stored in the result list.
Finally, we print the result list to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf("apple", "banana", "orange", "grape");
    val result = list.filter { it.length > 5 };
    println(result);
}

Output

[banana, orange]

Summary

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