using System;

using System.Collections.Generic;

using System.Linq;

​

    public class MyClass

    {

        public MyClass(int index, string otherFields)

        {

            Index = index;

            OtherFields = otherFields;

        }

​

        public int Index { get; set; }

        public string OtherFields { get; set; }

    }

public class Program

{

    public static void Main()

    {

            var list = new List<MyClass>();

            list.Add(new MyClass(2, "2.1"));

            list.Add(new MyClass(2, "2.2"));

            list.Add(new MyClass(3, "3.1"));

            list.Add(new MyClass(4, "4.1"));

​

            var firstGroup = list.GroupBy(x => x.Index)

                .OrderBy(g => g.Key)

                .FirstOrDefault()

                .AsEnumerable();

​

            if (firstGroup != null)

                foreach (var myClass in firstGroup)

                    Console.WriteLine(myClass.OtherFields);

​

    }

}