using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var s = new List<SampleObject>();

​

            s.Add(new SampleObject

            {

                MsfId = 100,

                PgId = new List<string> { "A", "B", "C" },

            });

​

            s.Add(new SampleObject

          {

              MsfId = 101,

              PgId = new List<string> { "A", "B", "C" },

          });

​

            s.Add(new SampleObject

          {

              MsfId = 100,

              PgId = new List<string> { "l", "h", "m" },

          });

​

            var result = s.GroupBy(y => y.MsfId)

                        .Select(y => new SampleObject

                        {

                            MsfId = y.Key,

                            PgId = y.SelectMany(g => g.PgId).Distinct().ToList(),

                        }).ToList();

​

​

            foreach (var item in result)

            {

                Console.WriteLine(item.MsfId);

​

                foreach (var item1 in item.PgId)

                {

                    Console.WriteLine(item1);

                }

            }

​

        }

    }

​

    public class SampleObject

    {

        public int MsfId { get; set; }

        public List<string> PgId { get; set; }

        public List<string> DcId { get; set; }

    }

​