Kotlin Tutorials

Kotlin Set takeWhile()
Syntax & Examples

Set.takeWhile() extension function

The takeWhile() extension function in Kotlin returns a list containing the first elements that satisfy the given predicate.

Syntax of Set.takeWhile()

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

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

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

Parameters

ParameterOptional/RequiredDescription
predicaterequiredA function that takes an element and returns a Boolean indicating whether the element satisfies the predicate.

Return Type

Set.takeWhile() returns value of type List.


✐ Examples

1 Taking elements from a set of integers while they are less than 4

Using takeWhile() to get elements from a set of integers while they are less than 4.

For example,

  1. Create a set of integers.
  2. Use takeWhile() with a predicate that checks if the element is less than 4.
  3. Print the resulting list.

Kotlin Program

fun main() {
    val numbers = setOf(1, 2, 3, 4, 5)
    val result = numbers.takeWhile { it < 4 }
    println(result)
}

Output

[1, 2, 3]

2 Taking elements from a set of strings while their length is less than 4

Using takeWhile() to get elements from a set of strings while their length is less than 4.

For example,

  1. Create a set of strings.
  2. Use takeWhile() with a predicate that checks if the length of the string is less than 4.
  3. Print the resulting list.

Kotlin Program

fun main() {
    val strings = setOf("one", "two", "three", "four")
    val result = strings.takeWhile { it.length < 4 }
    println(result)
}

Output

[one, two]

3 Taking elements from a set of custom objects while they are younger than 30

Using takeWhile() to get elements from a set of custom objects while they are younger than 30.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use takeWhile() with a predicate that checks if the age of the person is less than 30.
  4. Print the resulting list.

Kotlin Program

data class Person(val name: String, val age: Int)

fun main() {
    val people = setOf(Person("Alice", 30), Person("Bob", 25), Person("Charlie", 35))
    val result = people.takeWhile { it.age < 30 }
    println(result)
}

Output

[Person(name=Bob, age=25)]

Summary

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