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How to delete elements from the Set in Scala?

Here, we are going to learn how to delete elements from Set in Scala with example programs?
Submitted by Shivang Yadav, on December 03, 2019

Scala Set

In Scala, a Set is a collection of elements of the same type. All elements of the set are unique i.e. no elements are allowed. Sets can be mutable as well as immutable.

Example:

    Set(1, 4, 5, 7, 12, 87, 213)

In Scala, you can remove elements from mutable as well as immutable sets. This operation is handled differently for both mutable as well as immutable sets.

1) Deleting elements from the Mutable Set

For deleting elements of a mutable set, we will use -= ,--=, retain, clear, remove.

-=	Deletes single element from set.
--=	Deletes multiple element from set.
retain	Deletes multiple element based on a certain condition.
clear	Deletes all elements of the set.
remove	Removes the specified element and return boolean value of operation done.

Example 1: use of -= and --= methods

object MyClass {
    def main(args: Array[String]) {
        val set = scala.collection.mutable.Set(2, 56, 577,12 , 46, 19, 90 , 32, 75, 81)
        println("The set is "+set)
        set -= 2;
        println("After deletion of one element, the set is "+set)
        set --= List(577, 12, 19);
        println("After deletion of multiple elements, the set is "+set)
    }
}

Output

The set is HashSet(32, 81, 577, 2, 19, 56, 90, 75, 12, 46)
After deletion of one element, the set is HashSet(32, 81, 577, 19, 56, 90, 75, 12, 46)
After deletion of multiple elements, the set is HashSet(32, 81, 56, 90, 75, 46)

Example 2:

object MyClass {
    def main(args: Array[String]) {
        val set = scala.collection.mutable.Set(2, 56, 577,12 , 46, 19, 90 , 32, 75, 81);
        println("The set is "+set)
        set.retain(_  >20);
        println("After deletion using retain, the set is "+set)
        set.remove(577)
        println("After deletion using remove, the set is "+set)
        set.clear()
        println("After deletion using clear, the set is "+set)
    }
}

Output

The set is HashSet(32, 81, 577, 2, 19, 56, 90, 75, 12, 46)
After deletion using retain, the set is HashSet(32, 81, 577, 56, 90, 75, 46)
After deletion using remove, the set is HashSet(32, 81, 56, 90, 75, 46)
After deletion using clear, the set is HashSet()

2) Deleting elements from the Immutable Sets

Element in an immutable set cannot be changed. So, for performing deletion operation on these types of the set we need to create a new copy for every operation. -- and - operations are valid.

Example:

object MyClass {
    def main(args: Array[String]) {
        val set = scala.collection.mutable.Set(2, 56, 577,12 , 46, 19, 90 , 32, 75, 81);
        println("The set is "+set)
        var set1 = set - 2;
        println("After deletion of one element, the set is "+set1)
        var set2 = set1 -- List(577, 12, 19);
        println("After deletion of multiple elements, the set is "+set2)
        var set3 = set2 - (81, 46)
        println("After deletion of multiple elements, the set is "+set2)
        var set4 = set3 -- Array(56, 90);
        println("After deletion of multiple elements, the set is "+set2)
    }
}

Output

The set is HashSet(32, 81, 577, 2, 19, 56, 90, 75, 12, 46)
After deletion of one element, the set is HashSet(32, 81, 577, 19, 56, 90, 75, 12, 46)
After deletion of multiple elements, the set is HashSet(32, 81, 56, 90, 75, 46)
After deletion of multiple elements, the set is HashSet(32, 81, 56, 90, 75, 46)
After deletion of multiple elements, the set is HashSet(32, 81, 56, 90, 75, 46)