How to Find Difference of Sets in Kotlin Easily

In Kotlin, you can find the difference of two sets using the subtract() function or the - operator. Both return a new set containing elements from the first set that are not in the second set.

Syntax

To find the difference between two sets in Kotlin, use either:

• set1.subtract(set2) - returns a new set with elements in set1 not in set2.
• set1 - set2 - a shorthand operator for the same operation.

kotlin

val difference = set1.subtract(set2)
// or
val difference = set1 - set2

Example

This example shows how to find the difference between two sets of numbers. It prints the elements that are in the first set but not in the second.

kotlin

fun main() {
    val set1 = setOf(1, 2, 3, 4, 5)
    val set2 = setOf(3, 4, 6)

    val difference1 = set1.subtract(set2)
    val difference2 = set1 - set2

    println("Difference using subtract(): $difference1")
    println("Difference using - operator: $difference2")
}

Output

Difference using subtract(): [1, 2, 5]
Difference using - operator: [1, 2, 5]

Common Pitfalls

One common mistake is expecting subtract() or - to modify the original set. These functions return a new set and do not change the original sets.

Also, sets do not allow duplicate elements, so the difference will never contain duplicates.

kotlin

fun main() {
    val set1 = mutableSetOf(1, 2, 3)
    val set2 = setOf(2)

    // Wrong: expecting set1 to change
    set1.subtract(set2)
    println("After subtract(): $set1") // set1 is unchanged

    // Correct: assign the result
    val newSet = set1.subtract(set2)
    println("New set after subtract(): $newSet")
}

Output

After subtract(): [1, 2, 3]
New set after subtract(): [1, 3]

Quick Reference

Operation	Description	Example
subtract()	Returns a new set with elements in first set not in second	set1.subtract(set2)
- operator	Shorthand for subtract()	set1 - set2
Original sets	Not modified by subtract or -	set1 and set2 remain unchanged

Key Takeaways

Use subtract() or - operator to find set difference in Kotlin.

These operations return a new set and do not change the original sets.

Set difference contains only elements unique to the first set.

Sets automatically handle duplicates, so no duplicates appear in the result.