using System;

using System.Collections.Generic;

using System.Linq;

    public class Operation

    {

        public int ID { get; set; }

        public long IDOperation { get; set; }

        public int IDDiagnosis { get; set; }

    }

public class Program

{

​

        public static List<Operation> InitOperList()

        {

            List<Operation> list = new List<Operation>();

            list.Add(new Operation() { ID = 1, IDOperation = 22, IDDiagnosis = 30 });

            list.Add(new Operation() { ID = 2, IDOperation = 22, IDDiagnosis = 40 });

            list.Add(new Operation() { ID = 1, IDOperation = 23, IDDiagnosis = 10 });

            list.Add(new Operation() { ID = 7, IDOperation = 23, IDDiagnosis = 50 });

            list.Add(new Operation() { ID = 3, IDOperation = 23, IDDiagnosis = 60 });

            return list;

        }

        public static void GetDict(List<Operation> list)

        {

            var res_g = (from dg in list

                 group new { dg.ID, dg.IDOperation, dg.IDDiagnosis } by dg.IDOperation

                 into dg_group

                 select dg_group);

            foreach (var x in res_g)

            {

                Console.WriteLine("Key: " + x.Key);

                foreach (var y in x)

                {

                    Console.WriteLine("{0} {1} {2}",y.ID,  y.IDOperation, y.IDDiagnosis); ;

                }

            }

        }

        public void Main()

        {

            List<Operation> list = InitOperList();

            GetDict(list);          

        }

}