How do I find differences between 2 lists

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I have two sets of lists and I wish to get the difference between the two lists but for my logic I do not seem to be getting expected results :

LIST A
A002
A75
B908
123456
672314
756213

LIST B
htg1
EDDIE1
EDDIE2
A002
A75
B908

Expected Results
To get all the new codes in List B that are not already maintained in the mapping list (List A)
This should give me all new items as below :

htg1
EDDIE1
EDDIE2

Current Output
When I apply LINQ logic for filtering I am getting all the items in List B :

htg1
EDDIE1
EDDIE2
A002
A75
B908

This is because this join query is returning 0 rows :

 List<string> joinItems = new List<string>();

joinItems = (from d1 in mappings
                         join d2 in references on d1.MappingId equals d2.CustCode
                         select d1.MappingId).ToList<string>();

Where mappings represents resultset for LIST A :

C#

List<Partner> mappings = GetMappingsAsModel();

and references represents resultset for LIST B :

C#

List<CustomerCode> references = GetCustomerCodes();

And to find the differences I am doing this :

C#

List<string> cuscodes = references.Select(x => x.CustCode.ToString()).ToList();
          
           
 var newItems = cuscodes.Except(joinItems);

            
int newCodes = cuscodes.Except(joinItems).Count();

What is wrong with my Join query above ?

What I have tried:

I have tried the following alternative but still get nothing since the join query is returning nothing :

var result = references.Where(p => !mappings.All(p2 => p2.MappingId == p.CustCode)).ToString().ToList();

Posted 31-May-21 22:45pm

Tshumore

Updated 1-Jun-21 0:41am

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BillWoodruff · Answer 1 · 2021-06-01T00:41:00

Solution 2

Quote:
Expected Results
To get all the new codes in List B that are not already maintained in the mapping list (List A) This should give me all new items as below :

htg1
EDDIE1
EDDIE2

This "translates" as:

List<string> diffBA = ListB.Except(ListA).ToList();

Get your two Lists in the right shape, and it's this simple.

Posted 1-Jun-21 0:41am

BillWoodruff

Updated 1-Jun-21 5:26am

v2

Comments

Richard Deeming 1-Jun-21 10:32am

You'd need a .ToList() on the end of that - .Except(...) returns an IEnumerable<T>. :)

BillWoodruff 1-Jun-21 11:27am

Thanks !

OriginalGriff · Answer 2 · 2021-05-31T23:23:00

If your join query is returning zero rows, then the MappingIds do not match the CustCode values.
If I try your code with pure strings:

C#

List<string> mappings = new List<string>() { "A002", "A75", "B908", "123456", "672314", "756213" };
List<string> references = new List<string>() { "htg1", "EDDIE1", "EDDIE2", "A002", "A75", "B908" };
List<string> joinItems = new List<string>();

joinItems = (from d1 in mappings
             join d2 in references on d1 equals d2
             select d1).ToList<string>();

Then I get what I expect: three strings "A002", "75", and "B908"

So ... start with the debugger, and look at exactly what your Lists contain, and what relation there is between the Ids and CustCodes - I'd suspect you want CustID instead of CustCode, but I have no access to your data, so I can't be sure.