Sorting Collections in Kotlin

Introduction

Sorting Collections is a fundamental concept every Kotlin developer should understand. List, Map, and Set are the three core collection types. Choose List for ordered sequences, Set for unique elements, and Map for key-value lookups.

Sorted and sortedBy return sorted copies of collections. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• sorted and sortedBy return sorted copies of collections.
• sort/sortBy can sort mutable lists in place.
• Comparator logic can be customized.

Syntax

list.sorted()
list.sortedBy { it.name }

Sorting Collections in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val names = listOf("Ravi", "Anu", "Kumar")
    println(names.sorted())
}

Sample Output

[Anu, Kumar, Ravi]

When to use

Pick List for ordered data, Set when uniqueness matters, Map when you look up values by a key.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val names = listOf("Ravi", "Anu", "Kumar") assigns or updates a value used later in the program.

3. The println(names.sorted()) statement writes a line to the console — this produces part of the sample output below.

4. Sorted and sortedBy return sorted copies of collections.

5. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

Common Mistakes

Key Points

• sorted and sortedBy return sorted copies of collections.
• sort/sortBy can sort mutable lists in place.
• Comparator logic can be customized.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.