C# LINQ code for two list compare and replace

Question

I have two list of object 'User',

    User u1 = new User { Id = 1, Name = "user1" };
    User u2 = new User { Id = 2, Name = "user2" };
    User u3 = new User { Id = 3, Name = "user3" };
    User u3_1 = new User { Id = 10, Name = "user3" };
    User u5 = new User { Id = 5, Name = "user5" };
    User u6 = new User { Id = 6, Name = "user6" };

    List<User> listOld = new List<User> { u1, u2, u3 };
    List<User> listNew = new List<User> { u1, u2, u3_1, u5, u6 };

u3 and u3_1 is two objects which have same Name and different ID

I want to compare 'listOld' and 'listNew' by object's 'Name' property and get the Old object value to the 'listNew'.

final result should be

listNew = {u1, u2, u3, u5, u6}

if I say simply, compare the two list using list items's 'Name' and get the old object to the new list

I just want to know the LINQ code for this.

Thank you

Have you tried anything? It's good to show that you tried writing code before asking for it. This way you'll learn something and not just get a complete solution — MarcinJuraszek, Mar 26 '15 at 06:31
yes... i was able to compare two list by object wise ,but not object's property wise — Kasun Sameera Madhusanka, Mar 26 '15 at 06:33

score 2 · Accepted Answer · answered Mar 26 '15 at 07:24

2

Probably not the most efficient way, but this should work:

var result=listNew
  .GroupJoin(listOld,k1=>k1.Name,k2=>k2.Name,(k1,k2)=>
    new User {
      Id=k2.SingleOrDefault()==null?k1.Id:k2.SingleOrDefault().Id,
      Name=k2.SingleOrDefault()==null?k1.Name:k2.SingleOrDefault().Name
    }
  );

answered Mar 26 '15 at 07:24

Robert McKee

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You could simplify the GroupJoin by selecting both parts and then using a SelectMany with a DefaultIfEmpty to select the values from the new table if it didn't exist in the old table as well. – Robert McKee Mar 26 '15 at 07:31

C# LINQ code for two list compare and replace

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