Kotlin Tutorials

Kotlin Set withIndex()
Syntax & Examples

Set.withIndex() extension function

The withIndex() extension function in Kotlin returns a lazy Iterable that wraps each element of the original set into an IndexedValue containing the index of that element and the element itself.

Syntax of Set.withIndex()

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

fun <T> Set<T>.withIndex(): Iterable<IndexedValue<T>>

This withIndex() extension function of Set returns a lazy Iterable that wraps each element of the original set into an IndexedValue containing the index of that element and the element itself.

Return Type

Set.withIndex() returns value of type Iterable>.


✐ Examples

1 Using withIndex with a set of integers

Using withIndex() to iterate over a set of integers with their indices.

For example,

  1. Create a set of integers.
  2. Use withIndex() to wrap each element with its index.
  3. Iterate over the resulting Iterable and print each IndexedValue.

Kotlin Program

fun main() {
    val numbers = setOf(10, 20, 30)
    for ((index, value) in numbers.withIndex()) {
        println("Index: $index, Value: $value")
    }
}

Output

Index: 0, Value: 10
Index: 1, Value: 20
Index: 2, Value: 30

2 Using withIndex with a set of strings

Using withIndex() to iterate over a set of strings with their indices.

For example,

  1. Create a set of strings.
  2. Use withIndex() to wrap each element with its index.
  3. Iterate over the resulting Iterable and print each IndexedValue.

Kotlin Program

fun main() {
    val strings = setOf("apple", "banana", "cherry")
    for ((index, value) in strings.withIndex()) {
        println("Index: $index, Value: $value")
    }
}

Output

Index: 0, Value: apple
Index: 1, Value: banana
Index: 2, Value: cherry

3 Using withIndex with a set of custom objects

Using withIndex() to iterate over a set of custom objects with their indices.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use withIndex() to wrap each element with its index.
  4. Iterate over the resulting Iterable and print each IndexedValue.

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))
    for ((index, person) in people.withIndex()) {
        println("Index: $index, Person: $person")
    }
}

Output

Index: 0, Person: Person(name=Alice, age=30)
Index: 1, Person: Person(name=Bob, age=25)
Index: 2, Person: Person(name=Charlie, age=35)

Summary

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