Set Operations in Kotlin

Introduction

Set Operations 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.

Set stores unique elements. 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

• Set stores unique elements.
• Union, intersect and subtract operations are available.
• Useful for membership and comparison tasks.

Syntax

set1.union(set2)

Set Operations in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val a = setOf(1, 2, 3)
    val b = setOf(3, 4, 5)
    println("Union: ${a union b}")
    println("Intersect: ${a intersect b}")
}

Sample Output

Union: [1, 2, 3, 4, 5]
Intersect: [3]

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 a = setOf(1, 2, 3) assigns or updates a value used later in the program.

3. val b = setOf(3, 4, 5) assigns or updates a value used later in the program.

4. The println("Union: ${a union b}") statement writes a line to the console — this produces part of the sample output below.

5. The println("Intersect: ${a intersect b}") statement writes a line to the console — this produces part of the sample output below.

6. Set stores unique elements.

7. 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

• Understand the core idea: set stores unique elements.
• Prefer readable names and small functions so examples map directly to real projects.
• Run and modify the example — change values and observe how the output changes.

Common Mistakes

• Skipping the example and only reading the definition — hands-on practice cements the concept.
• Copying syntax without understanding nullable vs non-nullable types or scope rules.
• Ignoring compiler warnings that often point to safer alternatives.

Key Points

• Set stores unique elements.
• Union, intersect and subtract operations are available.
• Useful for membership and comparison tasks.
• 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.