How to Remove Duplicate Values From an Array in C#?

To remove duplicate values from an array in C#, you can use different approaches based on your requirements. So to do this we use the Distinct() function. HashSet, Using a Loop.This function gives distinct values from the given sequence. This method will throw ArgumentNullException if the given array is null.  

Example:

Input: int[] arr = { 1, 2, 2, 3, 4, 4, 5 }
Output: 1,2,3,4,5

Choose the approach based on readability, performance requirements, or your familiarity with C#. Generally, LINQ and HashSet approaches are more concise and easier to understand.

1.Distinct() Function

LINQ offers the Distinct() method to easily remove duplicates from an array.

Syntax:

array_name.Distinct()

Example:

//C# program that demonstrates how to retrieve unique values from an array using the Distinct method
using System;
using System.Linq;

class Program {
    static void Main()
    {
        int[] arr = { 1, 2, 2, 3, 4, 4, 5 };

        // Use Distinct to get unique values
        int[] distinct = arr.Distinct().ToArray();

        foreach(int x in distinct)
        {
            Console.Write(x+" ");
        }
    }
}

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Explanation:

• The Distinct() method removes duplicates.
• ToArray() converts the result back to an array.

2.Using HashSet<T>

The HashSet class automatically removes duplicates because it only allows unique values.

Syntax:

HashSet<int> s = new HashSet<int>(array);

Example:

//C# program that demonstrates how to retrieve unique values from an array using a HashSet. 
using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int[] arr = { 1, 2, 2, 3, 4, 4, 5 };
        HashSet<int> set = new HashSet<int>(arr);
        foreach (int num in set)
        {
            Console.Write(num + " ");
        }
    }
}

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Explanation:

• A HashSet is created using the original array, which removes duplicates.
• The HashSet is then copied to a new array to maintain the array format.

3.Using a Loop

You can use a loop to iterate through the array and add elements to a list if they haven’t already been added.

//C# programs that demonstrate how to retrieve unique values from an array using a List
using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        int[] arr = { 1, 2, 2, 3, 4, 4, 5 };
        List<int> distinctList = new List<int>();

        foreach (int num in arr)
        {
            if (!distinctList.Contains(num))
            {
                distinctList.Add(num);
            }
        }
        foreach (int num in distinctList)
        {
            Console.Write(num + " ");
        }
    }
}

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Explanation:

• Iterate through each element of the original array.
• Add it to the list only if it doesn’t already exist in the list (!uniqueList.Contains(value)).
• Finally, convert the list to an array using ToArray().