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

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);
			}
		}
	}
}

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);
			}
		}
	}
}