Question

I have an class which contains the following properties:

public class SomeClass()
{
public Int32 ObjectId1 {get;set;}
public Int32 ObjectId2 {get;set;}
public Int32 ActiveThickeness {get;set;}
public Int32 ActiveFilterThickness {get;set;}
}

I also have 2 lists:

List<SomeClass> A
List<SomeClass> B

List A has data:

| ObjectId1 | ObjectId2 | ActiveThickness | ActiveFilterThickness |
-------------------------------------------------------------------
|     1     |     3     |       50        |           0           |
 ------------------------------------------------------------------
|     1     |     2     |       400       |           0           |
-------------------------------------------------------------------
|     4     |    603    |       27        |           0           |
-------------------------------------------------------------------

List B has data:

| ObjectId1 | ObjectId2 | ActiveThickness | ActiveFilterThickness |
-------------------------------------------------------------------
|     1     |     3     |       0         |         13671         |
 ------------------------------------------------------------------
|     1     |     2     |       0         |          572          |
-------------------------------------------------------------------
|    29     |    11     |       0         |         4283          |
-------------------------------------------------------------------

I want to merge A and B (using LINQ if possible) into List C of SomeCalss which contains data as followed:

| ObjectId1 | ObjectId2 | ActiveThickness | ActiveFilterThickness |
-------------------------------------------------------------------
|     1     |     3     |       50        |         13671         |
 ------------------------------------------------------------------
|     1     |     2     |       400       |          572          |
-------------------------------------------------------------------
|    29     |    11     |       0         |         4283          |
-------------------------------------------------------------------
|     4     |    603    |       27        |           0           |
-------------------------------------------------------------------

How can I achieve that?

Answer 1

Use GroupBy to group common objects and Sum to sum required properties

        var ab = A.Concat(B).GroupBy(x => new
                                              {
                                                      x.ObjectId1,
                                                      x.ObjectId2
                                              });


        var result = ab.Select(x => new SomeClass
                                        {
                                                ObjectId1 = x.Key.ObjectId1,
                                                ObjectId2 = x.Key.ObjectId2,
                                                ActiveFilterThickness = x.Sum(i => i.ActiveFilterThickness),
                                                ActiveThickeness = x.Sum(i => i.ActiveThickeness)
                                        });