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 :

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) 
} 

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 :

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)  
}  

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 –

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")) 
} 

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 –

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()) 
} 

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 .

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 ) 
}  

Output:

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 –

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")))  
}  

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 –

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 
} 

Output :

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

My Personal Notes

Suggest a Topic

Adding and removing elements in a set –

Set Indexing –

Set first and last element –

Traversal in a mutableSet –

contains() and containsAll() functions –

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

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