Working with Set

In this lesson you will learn how to hold duplicate-free data with Set in Kotlin, and understand the basics of the set data structure. This is for anyone searching for "Kotlin Set how to use".

Set is a box that refuses to hold the same value twice. It is handy for stripping duplicates out of an array, or for checking membership quickly.

The sample code builds a set from the duplicate-containing list [1, 2, 2, 3, 3, 3] with .toSet(); the duplicates disappear automatically and only 1, 2, and 3 remain. Notice how contains() checks whether a value is present.

A common stumbling block for beginners is that the order of a Set is not guaranteed. Unlike a list, items are not necessarily kept in insertion order, so a list is a better fit when order matters.

In real-world development, Set's contains() also outperforms a list's once there is a lot of data, making it very handy for removing duplicates.

📖 Reference code

fun main() {
    val nums = listOf(1, 2, 2, 3, 3, 3)
    val uniqueNums = nums.toSet()
    println(uniqueNums.sorted())
    println(uniqueNums.contains(2))
}

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