C# | Number of elements in HashSet

Last Updated : 12 Jul, 2023

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. You can use HashSet.Count Property to count the number of elements in a HashSet.

Syntax:

mySet.Count;

Here mySet is the HashSet Below given are some examples to understand the implementation in a better way:

Example 1:

CSHARP

// C# code to get the number of
// elements that are contained in HashSet
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

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

        // Inserting elements in HashSet
        for (int i = 0; i < 5; i++) {
            mySet.Add(i * 2);
        }

        // To get the number of
        // elements that are contained in HashSet
        Console.WriteLine(mySet.Count);
    }
}

Output

Example 2:

CSHARP

// C# code to get the number of
// elements that are contained in HashSet
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

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

        // To get the number of
        // elements that are contained in HashSet.
        // Note that, here the HashSet is empty
        Console.WriteLine(mySet.Count);
    }
}

Output

Using the AsEnumerable and Count methods

AsEnumerable: The AsEnumerable method is used to convert a collection into an enumerable type, enabling the use of LINQ extension methods.
Count: The Count method returns the number of elements in a collection, providing a convenient way to determine its size.

using System;
using System.Collections.Generic;
using System.Linq;

public class GFG
{
    static public void Main()
    {
        // Create a HashSet
        HashSet<int> numbers = new HashSet<int>();
        numbers.Add(1);
        numbers.Add(2);
        numbers.Add(3);

        // Get the count of elements using the Enumerable.Count() method
        int elementCount = numbers.AsEnumerable().Count();

        // Display the result
        Console.WriteLine("Number of elements in the HashSet: " + elementCount);
    }
}

Output

Number of elements in the HashSet: 3

In this code, we create a HashSet called numbers and add three integer values to it. Then, we use the AsEnumerable() method to convert the HashSet to an IEnumerable<int>, and the Count() method from the Enumerable class to get the count of elements in the HashSet. The main heading is printed, followed by the elements of the HashSet and the count of elements.

C# | Add element to HashSet

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