Kotlin Tutorials

Kotlin Set filterIndexed()
Syntax & Examples

Set.filterIndexed() extension function

The filterIndexed() extension function for sets in Kotlin returns a list containing only elements of the set that match the given predicate, with the predicate having access to the index of each element.

Syntax of Set.filterIndexed()

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

fun <T> Set<T>.filterIndexed(predicate: (index: Int, T) -> Boolean): List<T>

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

Parameters

ParameterOptional/RequiredDescription
predicaterequiredA function that takes the index and an element of the set and returns a Boolean indicating whether the element matches the condition.

Return Type

Set.filterIndexed() returns value of type List.


✐ Examples

1 Using filterIndexed() to get elements with even indices from a set

In Kotlin, we can use the filterIndexed() function to get a list of elements from a set of integers that are at even indices.

For example,

  1. Create a set of integers.
  2. Use the filterIndexed() function with a predicate that checks if the index is even.
  3. Print the resulting list to the console using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val numbers = setOf(1, 2, 3, 4, 5, 6)
    val evenIndexElements = numbers.filterIndexed { index, _ -> index % 2 == 0 }
    println("Elements at even indices: $evenIndexElements")
}

Output

Elements at even indices: [1, 3, 5]

2 Using filterIndexed() with a set of strings

In Kotlin, we can use the filterIndexed() function to get a list of strings from a set that are at odd indices.

For example,

  1. Create a set of strings.
  2. Use the filterIndexed() function with a predicate that checks if the index is odd.
  3. Print the resulting list to the console using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val fruits = setOf("apple", "banana", "cherry", "date")
    val oddIndexFruits = fruits.filterIndexed { index, _ -> index % 2 != 0 }
    println("Fruits at odd indices: $oddIndexFruits")
}

Output

Fruits at odd indices: [banana, date]

3 Using filterIndexed() with an empty set

In Kotlin, we can use the filterIndexed() function on an empty set, which will return an empty list regardless of the predicate.

For example,

  1. Create an empty set of integers.
  2. Use the filterIndexed() function with a predicate that checks if the index is even.
  3. Print the resulting list to the console using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val emptySet = emptySet<Int>()
    val filteredElements = emptySet.filterIndexed { index, _ -> index % 2 == 0 }
    println("Filtered elements in empty set: $filteredElements")
}

Output

Filtered elements in empty set: []

Summary

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