using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var fun = new List<Data>();

        fun.Add(new Data() { Code ="X0000", GroupLevel=4, Group = null});

        fun.Add(new Data() { Code ="X1000", GroupLevel=3, Group = "X0000"});

        fun.Add(new Data() { Code ="X2000", GroupLevel=3, Group = "X0000"});

        fun.Add(new Data() { Code ="X3000", GroupLevel=3, Group = "X0000"});

        fun.Add(new Data() { Code ="X1100", GroupLevel=2, Group = "X1000"});

        fun.Add(new Data() { Code ="X1200", GroupLevel=2, Group = "X1000"});

        fun.Add(new Data() { Code ="X1300", GroupLevel=2, Group = "X1000"});

        fun.Add(new Data() { Code ="X2100", GroupLevel=2, Group = "X2000"});

        fun.Add(new Data() { Code ="X2200", GroupLevel=2, Group = "X2000"});

        fun.Add(new Data() { Code ="X2300", GroupLevel=2, Group = "X2000"});

        fun.Add(new Data() { Code ="X1110", GroupLevel=1, Group = "X1100"});

        fun.Add(new Data() { Code ="X1120", GroupLevel=1, Group = "X1100"});

        fun.Add(new Data() { Code ="X1111", GroupLevel=0, Group = "X1110"});

        fun.Add(new Data() { Code ="X1112", GroupLevel=0, Group = "X1110"});

        fun.Add(new Data() { Code ="X1113", GroupLevel=0, Group = "X1110"});

        fun.Add(new Data() { Code ="X1114", GroupLevel=0, Group = "X1110"});

        var result = (from f1 in fun

                     join f2 in fun on f1.Code equals (f2.Group ?? f2.Code)

                      orderby f2.Code

                     select f2).Select((v,i) => new Data(v,i)).ToList();

        result.ForEach(x => Console.WriteLine(x));

    }

}

​

public class Data

{

    public int Seq {get;set;}

    public string Code {get;set;}

    public int GroupLevel {get;set;}

    public string Group {get;set;}

    public Data(){}

    public Data(Data v, int i)

    {

        Seq = i+1;

        Code = v.Code;

        GroupLevel = v.GroupLevel;

        Group = v.Group;

    }

    public override string ToString()

    {

        return string.Format("{3} - {0} - {1} - {2}",Code, GroupLevel,Group, Seq);

    }

}

​

​