Kotlin List takeWhile()
Syntax & Examples

Syntax of List.takeWhile()

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

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

This takeWhile() extension function of List returns a list containing first elements satisfying the given predicate.

✐ Examples

1 Example

In this example,

We create a list of integers named list1 with elements 1, 2, 3, 4, 5.
We use the takeWhile function with a predicate { it < 3 } on list1 to take elements until the predicate condition is no longer satisfied.
The result is a new list containing elements until the first element < 3, which is [1, 2].
We print the result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1, 2, 3, 4, 5)
    val result = list1.takeWhile { it < 3 }
    println(result)
}

Output

[1, 2]

2 Example

In this example,

We create a list of characters named list1 with elements 'a', 'b', 'c', 'd', 'e'.
We use the takeWhile function with a predicate { it < 'd' } on list1 to take elements until the predicate condition is no longer satisfied.
The result is a new list containing elements until the first element < 'd', which is [a, b, c].
We print the result using println().

Kotlin Program

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

Output

[a, b, c]

3 Example

In this example,

We create a list of strings named list1 with elements "apple", "banana", "cherry", "date", "elderberry".
We use the takeWhile function with a predicate { it.length <= 6 } on list1 to take elements until the predicate condition is no longer satisfied.
The result is a new list containing elements until the length of an element is not less than or equal to 6 characters, which is ["apple", "banana", "cherry"].
We print the result using println().

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry", "date", "elderberry")
    val result = list1.takeWhile { it.length <= 6 }
    println(result)
}

Output

[apple, banana, cherry, date]

Summary

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