Kotlin Tutorials

Kotlin Set toSortedSet()
Syntax & Examples

toSortedSet() extension function

The toSortedSet() extension function in Kotlin returns a new SortedSet containing all elements of the collection, sorted according to the specified comparator.

Syntax of toSortedSet()

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

fun <T> Iterable<T>.toSortedSet(comparator: Comparator<in T>): SortedSet<T>

This toSortedSet() extension function of Set returns a new SortedSet of all elements.

Parameters

ParameterOptional/RequiredDescription
comparatorrequiredThe comparator used to determine the order of the elements in the sorted set.

Return Type

Set.toSortedSet() returns value of type SortedSet.


✐ Examples

1 Converting a set of integers to a SortedSet

Using toSortedSet() to convert a set of integers to a SortedSet in descending order.

For example,

  1. Create a set of integers.
  2. Use toSortedSet() with a comparator to sort the set in descending order.
  3. Print the resulting SortedSet.

Kotlin Program

fun main() {
    val intSet = setOf(1, 2, 3, 4, 5)
    val sortedSet = intSet.toSortedSet(compareByDescending { it })
    println(sortedSet)
}

Output

[5, 4, 3, 2, 1]

2 Converting a set of strings to a SortedSet

Using toSortedSet() to convert a set of strings to a SortedSet by string length.

For example,

  1. Create a set of strings.
  2. Use toSortedSet() with a comparator to sort the set by string length.
  3. Print the resulting SortedSet.

Kotlin Program

fun main() {
    val stringSet = setOf("one", "two", "three", "four")
    val sortedSet = stringSet.toSortedSet(compareBy { it.length })
    println(sortedSet)
}

Output

[one, two, four, three]

3 Converting a set of custom objects to a SortedSet

Using toSortedSet() to convert a set of custom objects to a SortedSet by a custom property.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use toSortedSet() with a comparator to sort the set by a custom property.
  4. Print the resulting SortedSet.

Kotlin Program

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

fun main() {
    val peopleSet = setOf(Person("Alice", 30), Person("Bob", 25), Person("Charlie", 35))
    val sortedSet = peopleSet.toSortedSet(compareBy { it.age })
    println(sortedSet)
}

Output

[Person(name=Bob, age=25), Person(name=Alice, age=30), Person(name=Charlie, age=35)]

Summary

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