Kotlin Sets

Introduction

Sets in Kotlin are unordered collections of unique elements.

Unlike lists, sets do not allow duplicate elements.

Kotlin provides two types of sets: Set for immutable sets and MutableSet for mutable sets.

This chapter will cover how to create and manipulate both immutable and mutable sets, along with common operations that can be performed on sets.

Immutable Sets

An immutable set cannot be modified after it is created. You can use the setOf function to create an immutable set.

Creating an Immutable Set

Syntax

val set: Set<Type> = setOf(elements)

Example

fun main() {
    val fruits: Set<String> = setOf("Apple", "Banana", "Cherry")
    println(fruits)
}

Explanation:

• val fruits: Set<String> = setOf("Apple", "Banana", "Cherry"): Creates an immutable set of strings.

Output:

[Apple, Banana, Cherry]

Mutable Sets

A mutable set can be modified after it is created. You can use the mutableSetOf function to create a mutable set.

Creating a Mutable Set

Syntax

val set: MutableSet<Type> = mutableSetOf(elements)

Example

fun main() {
    val fruits: MutableSet<String> = mutableSetOf("Apple", "Banana")
    fruits.add("Cherry")
    println(fruits)
}

Explanation:

• val fruits: MutableSet<String> = mutableSetOf("Apple", "Banana"): Creates a mutable set of strings.
• fruits.add("Cherry"): Adds an element to the mutable set.

Output:

[Apple, Banana, Cherry]

Common Set Operations

Kotlin provides various operations that can be performed on sets, such as checking membership, iterating through sets, adding/removing elements, and more.

Checking Membership

You can check if an element is in a set using the contains function or the in operator.

Example

fun main() {
    val fruits: Set<String> = setOf("Apple", "Banana", "Cherry")
    println("Apple" in fruits)          // Prints "true"
    println(fruits.contains("Banana"))  // Prints "true"
    println(fruits.contains("Mango"))   // Prints "false"
}

Output:

true
true
false

Iterating Through a Set

You can iterate through a set using a for loop.

Example

fun main() {
    val fruits: Set<String> = setOf("Apple", "Banana", "Cherry")
    for (fruit in fruits) {
        println(fruit)
    }
}

Output:

Apple
Banana
Cherry

Adding and Removing Elements (Mutable Set)

You can add and remove elements from a mutable set using various methods.

Example

fun main() {
    val fruits: MutableSet<String> = mutableSetOf("Apple", "Banana")
    fruits.add("Cherry")
    println(fruits) // Prints "[Apple, Banana, Cherry]"

    fruits.remove("Banana")
    println(fruits) // Prints "[Apple, Cherry]"
}

Output:

[Apple, Banana, Cherry]
[Apple, Cherry]

Union, Intersection, and Difference

Kotlin provides functions to perform union, intersection, and difference operations on sets.

Example

fun main() {
    val set1: Set<Int> = setOf(1, 2, 3)
    val set2: Set<Int> = setOf(3, 4, 5)

    val union = set1.union(set2)
    println("Union: $union") // Prints "[1, 2, 3, 4, 5]"

    val intersection = set1.intersect(set2)
    println("Intersection: $intersection") // Prints "[3]"

    val difference = set1.subtract(set2)
    println("Difference: $difference") // Prints "[1, 2]"
}

Output:

Union: [1, 2, 3, 4, 5]
Intersection: [3]
Difference: [1, 2]

Converting Set to List

You can convert a set to a list using the toList function.

Example

fun main() {
    val fruits: Set<String> = setOf("Apple", "Banana", "Cherry")
    val fruitList: List<String> = fruits.toList()
    println(fruitList)
}

Output:

[Apple, Banana, Cherry]

Example Program with Sets

Here is an example program that demonstrates various aspects of using sets in Kotlin:

fun main() {
    // Immutable set
    val fruits: Set<String> = setOf("Apple", "Banana", "Cherry")
    println(fruits)

    // Mutable set
    val mutableFruits: MutableSet<String> = mutableSetOf("Apple", "Banana")
    mutableFruits.add("Cherry")
    println(mutableFruits)

    // Checking membership
    println("Apple" in fruits)
    println(fruits.contains("Banana"))
    println(fruits.contains("Mango"))

    // Iterating through a set
    for (fruit in fruits) {
        println(fruit)
    }

    // Adding and removing elements (mutable set)
    mutableFruits.remove("Banana")
    println(mutableFruits)

    // Union, intersection, and difference
    val set1: Set<Int> = setOf(1, 2, 3)
    val set2: Set<Int> = setOf(3, 4, 5)

    val union = set1.union(set2)
    println("Union: $union")

    val intersection = set1.intersect(set2)
    println("Intersection: $intersection")

    val difference = set1.subtract(set2)
    println("Difference: $difference")

    // Converting set to list
    val fruitList: List<String> = fruits.toList()
    println(fruitList)
}

Output:

[Apple, Banana, Cherry]
[Apple, Banana, Cherry]
true
true
false
Apple
Banana
Cherry
[Apple, Cherry]
Union: [1, 2, 3, 4, 5]
Intersection: [3]
Difference: [1, 2]
[Apple, Banana, Cherry]

Conclusion

In this chapter, you learned about sets in Kotlin, including how to create and manipulate immutable and mutable sets. You also learned about common set operations such as checking membership, iterating through sets, adding/removing elements, and performing union, intersection, and difference operations.