using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<List_Data> List1 = new List<List_Data>();

        List1.Add(new List_Data{Material = "1", Batch = "B1", QTY = 5});

        List1.Add(new List_Data{Material = "1", Batch = "B2", QTY = 5});

        List1.Add(new List_Data{Material = "2", Batch = "B1", QTY = 15});

        List<List_Data> List2 = new List<List_Data>();

        List2.Add(new List_Data{Material = "1", Batch = "B1", QTY = 2});

        List2.Add(new List_Data{Material = "3", Batch = "B1", QTY = 5});

        List2.Add(new List_Data{Material = "3", Batch = "B2", QTY = 15});

        var result = List1

            .Select(e => new        

            {

                key = new

                {

                    e.Material, 

                    e.Batch

                }, 

                QTY = e.QTY

            })

            .Concat(List2

                .Select(e => new

                {

                    key = new

                    {

                        e.Material, 

                        e.Batch

                    }, 

                    QTY = -e.QTY

                }))

            .GroupBy( e => e.key, e => e.QTY )

            .Select(g => new Report_Class

            {

                Material = g.Key.Material, 

                Batch = g.Key.Batch, 

                Difference = g.Sum()

            })

            .ToList();

        foreach (var r in result)

        {

            Console.WriteLine("Material = {0}, Batch = {1}, Difference = {2}", r.Material, r.Batch, r.Difference);

        }

    }

}

​

public class List_Data

{

    public string Material

    {

        get;

        set;

    }

​

    public string Batch

    {

        get;

        set;

    }

​

    public int QTY

    {

        get;

        set;

    }

}

​

public class Report_Class

{

    public string Material

    {

        get;

        set;

    }

​

    public string Batch

    {

        get;

        set;

    }

​

    public int Difference

    {

        get;

        set;

    }

}