C# / .NET - merge two Lists into HashSet

In this article, we would like to show you how to merge two Lists into HashSet in C#.

Quick solution:

List<string> list1 = new List<string> { "A", "B", "C" };
List<string> list2 = new List<string> { "D", "B", "C" };

HashSet<string> alphabet = new HashSet<string>(list1);

alphabet.UnionWith(list2);

Practical example

In this example, we merge list1 and list2 Lists into alphabet HashSet using UnionWith() method.

using System;
using System.Collections.Generic;

public class Program
{
    public static void Main()
    {
        List<string> list1 = new List<string> { "A", "B", "C" };
        List<string> list2 = new List<string> { "D", "B", "C" };

        // initialize hashset with list1 on creation
        HashSet<string> alphabet = new HashSet<string>(list1);

        // add list2
        alphabet.UnionWith(list2);

        // print items
        foreach (string item in alphabet)
            Console.WriteLine(item);
    }
}

Output:

A
B
C
D

Note:

Merging two Lists into a HashSet removes duplicate elements.

References

1. HashSet<T>.UnionWith(IEnumerable<T>) Method (System.Collections.Generic) | Microsoft Docs