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.