How to Remove Duplicates from List in C# Easily

To remove duplicates from a list in C#, use list.Distinct() from LINQ which returns unique elements. Alternatively, convert the list to a HashSet which automatically removes duplicates.

Syntax

Use Distinct() method from LINQ to get unique elements from a list. It returns an IEnumerable of distinct items.

Alternatively, create a HashSet<T> from the list which stores only unique values.

csharp

var uniqueList = list.Distinct().ToList();

var uniqueSet = new HashSet<T>(list);

Example

This example shows how to remove duplicates from a list of integers using Distinct() and HashSet. Both methods produce a list with unique values.

csharp

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

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

        // Using Distinct()
        List<int> distinctList = numbers.Distinct().ToList();
        Console.WriteLine("Using Distinct(): " + string.Join(", ", distinctList));

        // Using HashSet
        HashSet<int> uniqueSet = new HashSet<int>(numbers);
        Console.WriteLine("Using HashSet: " + string.Join(", ", uniqueSet));
    }
}

Output

Using Distinct(): 1, 2, 3, 4, 5
Using HashSet: 1, 2, 3, 4, 5

Common Pitfalls

• Forgetting to call ToList() after Distinct() if you need a list instead of IEnumerable.
• Using HashSet changes the order of elements because it does not preserve insertion order.
• Modifying the original list while iterating can cause errors.

csharp

/* Wrong: Using Distinct() but not converting to list when list needed */
var distinctEnumerable = numbers.Distinct();
// distinctEnumerable is IEnumerable<int>, not List<int>

/* Right: Convert to list */
var distinctList = numbers.Distinct().ToList();

Quick Reference

Use Distinct() for simple unique filtering with order preserved. Use HashSet for fast uniqueness but unordered results.

Method	Description	Order Preserved	Return Type
Distinct()	Returns unique elements preserving order	Yes	IEnumerable
HashSet	Stores unique elements, fast lookup, unordered	No	HashSet

Key Takeaways

Use list.Distinct().ToList() to get a list without duplicates while keeping order.

HashSet removes duplicates but does not keep the original order.

Always convert Distinct() result to a list if you need list methods.

Avoid modifying a list while iterating to prevent errors.

Choose the method based on whether order matters and performance needs.