C# | Check if a HashSet is a subset of the specified collection

Last Updated : 11 Jul, 2025

A HashSet is an unordered collection of the unique elements. It is found in System.Collections.Generic namespace. It is used in a situation where we want to prevent duplicates from being inserted in the collection. As far as performance is concerned, it is better in comparison to the list. HashSet.IsSubsetOf(IEnumerable) Method is used to check whether a HashSet object is a subset of the specified collection. Syntax:

mySet1.IsSubsetOf(mySet2);

Here mySet1 and mySet2 are HashSets. Return Type: This method returns true if the HashSet object is a subset of another subset otherwise, false. Exception: This method will give ArgumentNullException if the HashSet is null. Below given are some examples to understand the implementation in a better way: Example 1:

CSHARP

// C# code to Check if a HashSet is
// a subset of the specified collection
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of integers
        HashSet<int> mySet1 = new HashSet<int>();

        // Inserting elements in HashSet
        // mySet1 only contains even numbers less than
        // equal to 10
        for (int i = 1; i <= 5; i++)
            mySet1.Add(2 * i);

        // Creating a HashSet of integers
        HashSet<int> mySet2 = new HashSet<int>();

        // Inserting elements in HashSet
        // mySet2 contains all numbers from 1 to 10
        for (int i = 1; i <= 10; i++)
            mySet2.Add(i);

        // Check if a HashSet mySet1 is a subset
        // of the HashSet mySet2
        Console.WriteLine(mySet1.IsSubsetOf(mySet2));
    }
}

Output:

True

Example 2:

CSHARP

// C# code to Check if a HashSet is
// a subset of the specified collection
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of integers
        HashSet<int> mySet1 = new HashSet<int>();

        // Creating a HashSet of integers
        HashSet<int> mySet2 = new HashSet<int>();

        // Inserting elements in HashSet mySet2.
        // mySet2 contains all numbers from 1 to 10
        for (int i = 1; i <= 10; i++)
            mySet2.Add(i);

        // Check if a HashSet mySet1 is a subset
        // of the HashSet mySet2
        // It should return true, as an empty HashSet is
        // subset of other HashSet
        Console.WriteLine(mySet1.IsSubsetOf(mySet2));
    }
}