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How to remove all elements from the HashSet in C#

Surabhi Sharma

The HashSet<T> generic class in the System.Collections.Generic namespace provides the Clear() method, which is used to remove all the elements from a HashSet in C#. The HashSet<T> becomes empty after the Clear() method is called.

Syntax

public void Clear ();
  • Other object references from elements of the HashSet<T> are also released after calling the Clear() method.

  • The HashSet’s Count property becomes 0zero after the Clear() method is called.

  • This method does not change the capacity of the HashSet.

  • This method changes the state of the HashSet.

In the example below, we first create a HashSet of strings and add two strings to it: January and February. We then print the count of elements in the HashSet.

Next, we call the Clear() method to remove all elements of the HashSet. We again print the count and observe zero after the Clear() method is called.

The program prints the following output and exits.

Added 'January' and 'February' to HashSet, Count : 2
Count of HashSet afte Clear() : 0
using System;
using System.Collections.Generic;

class HashSetAdd
{
    static void Main()
    {
       HashSet<string> monthSet = new HashSet<string>();
       monthSet.Add("January");
       monthSet.Add("February");
       Console.WriteLine($"Added 'January' and 'February' to HashSet, Count : {monthSet.Count}");
       monthSet.Clear();
       Console.WriteLine($"Count of HashSet afte Clear() : {monthSet.Count}");
    }
}

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