Knowledge Base

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====== Remove Duplicates From List Collection ======

A couple of examples of removing duplicate entries in list collections in C#:

===== Implemented As a Method =====

<file csharp remove-dups-method.cs>
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;

namespace Console1
{
	class Program
	{

		static IEnumerable<T> RemoveDuplicates<T>(List<T> inputList)
		{
			inputList.Sort();

			return inputList.Distinct();
		}

		static void Main(string[] args)
		{
			var myList = new List<string> {
				"John",
				"Andrew",
				"James",
				"Jack",
				"Andrew",
				"Bob",
				"Jack"
			};

			var newList = RemoveDuplicates(myList);

			foreach (var item in newList)
			{
				Console.WriteLine(item);
			}
		}
	}
}
</file>

===== Implemented As An Extension =====

<file csharp remove-dups-extension.cs>
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;

namespace Console1
{
	public static class ListExtension
	{
		public static IEnumerable<T> RemoveDuplicates<T>(this List<T> inputList)
		{
			inputList.Sort();

			return inputList.Distinct();
		}
	}

	class Program
	{
		static void Main(string[] args)
		{
			var myList = new List<string> {
				"John",
				"Andrew",
				"James",
				"Jack",
				"Andrew",
				"Bob",
				"Jack"
			};

			var newList = myList.RemoveDuplicates();

			foreach (var item in newList)
			{
				Console.WriteLine(item);
			}
		}
	}
}
</file>

{{tag>dotnet}}