Kotlin mutableSetOf() method

Kotlin Set interface is a generic unordered collection of elements and it does not contain duplicate elements. Kotlin supports two types of sets mutable and immutable.

setOf() is immutable means it supports only read-only functionalities and mutableSetOf() is mutable means it supports read and write both functionality.

Syntax:

fun <T> mutableSetOf( vararg elements: T): MutableSet<T>

Description:

  • This function returns a set of given elements, which can be both read and written.
  • The returned set preserves the element iteration order.

Kotlin porogram of mutableSetOf() function :

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fun main(args: Array<String>)
{
    //declaring a mutable set of integers
    val mutableSetA = mutableSetOf<Int>( 1 , 2 , 3 , 4 , 3);
    println(mutableSetA)
  
    //declaring a mutable set of strings
    val mutableSetB = mutableSetOf<String>("Geeks","for" , "geeks");
    println(mutableSetB)
  
    //declaring an empty mutable set of integers
    val mutableSetC = mutableSetOf<Int>()
    println(mutableSetC)
}

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Output:

[1, 2, 3, 4]
[Geeks, for, geeks]
[]

Adding and removing elements in a set –

We can add elements in a mutable set using the add() function, and remove an elements using remove () function.

Example :

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fun main(args: Array<String>) 
    //declaring a mutable set of integers
    val seta = mutableSetOf( 1 , 2 , 3 , 4 , 3);
    println(seta);
    //adding elements 6 & 7
    seta.add(6);
    seta.add(7);
    println(seta);
       
    //removing 3 from the set
    seta.remove(3);
    println(seta);
       
    //another way to add elements is by using listOf() function
    seta += listOf(8,9)
    println(seta) 

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Output:

[1, 2, 3, 4]
[1, 2, 3, 4, 6, 7]
[1, 2, 4, 6, 7]
[1, 2, 4, 6, 7, 8, 9]

Set Indexing –

Using index functions indexOf() , lastIndexOf() we can get the index of the specified element. And we can also find the elements at some specific index using elementAt() function.

Kotlin program of using index –

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fun main(args: Array<String>) {
  
    val captains = mutableSetOf("Kohli","Smith","Root","Malinga","Rohit","Dhawan")
  
    println("The element at index 2 is: "+captains.elementAt(2))
  
    println("The index of element is: "+captains.indexOf("Smith"))
  
    println("The last index of element is: "+captains.lastIndexOf("Rohit"))
}

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Output:

The element at index 2 is: Root
The index of element is: 1
The last index of element is: 4

Set first and last element –

We can get the first and element of a set using first() and last() functions.
Kotlin program –

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fun main(args: Array<String>){
    val captains = mutableSetOf(1,2,3,4,"Kohli","Smith",
        "Root","Malinga","Dhawan","Rohit")
  
    println("The first element of the set is: "+captains.first())
  
    println("The last element of the set is: "+captains.last())
}

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Output:

The first element of the set is: 1
The last element of the set is: Dhawan

Traversal in a mutableSet –

We can run a for loop with an iterator which traverse all the items in the set .

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fun main(args: Array<String>) 
    //declaring a mutable set of integers
    val seta = mutableSetOf( 1 , 2 , 3 , 4 , 3);
   
    //traversal of seta using an iterator 'item'
    for(item in seta) 
        println( item )

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Output:

1
2
3
4

contains() and containsAll() functions –

Both the methods are used to check whether an element is present in the set or not?
Kotlin program of using contains() and containsAll() function –

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fun main(args: Array<String>){ 
    val captains = mutableSetOf(1,2,3,4,"Kohli","Smith"
        "Root","Malinga","Rohit","Dhawan"
    
    
    var name = "Dhawan"
    println("The set contains the element $name or not?"
            "   "+captains.contains(name)) 
    
    var num = 5
    println("The set contains the element $num or not?"
            "   "+captains.contains(num)) 
    
    println("The set contains the given elements or not?"
            "   "+captains.containsAll(setOf(1,3,"Root"))) 

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Output:

The set contains the element Dhawan or not?   true
The set contains the element 5 or not?   false
The set contains the given elements or not?   true

Checking equality of empty sets and use of isEmpty() functions –

fun <T> mutableSetOf(): mutableSet<T>

This syntax returns an empty set of specific type.

Kotlin program of using isEmpty() function –

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fun main(args: Array<String>) {
    //creating an empty set of strings
    val seta = mutableSetOf<String>()
    //creating an empty set of integers
    val setb = mutableSetOf<Int>()
   
   
    //checking if set is empty or not
    println("seta.isEmpty() is ${seta.isEmpty()}")
   
    // Since Empty sets are equal
   
    //checking if two sets are equl or not
    println("seta == setb is ${seta == setb}")
   
    println(seta) //printing first set
}

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Output :

seta.isEmpty() is true
seta == setb is true
[]


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