Question

I’m after some help with some Visual Studio C# code.

I have a data table with some rows & data like below:

Id      CodeNum     LineNum
1023503     4001        1
1023504     4001        1
1023505     4001        1
1023506     4002        1
1023507     4002        1
1023508     4002        1
1023509     4002        1
1023510     4003        2
1023511     4003        2
1023512     4003        2
1023513     4003        2
1023514     4004        2
1023515     4004        2
1023516     4005        3
1023517     4005        3
1023518     4006        3
1023519     4006        3
1023520     4006        3
1023521     4007        4
1023522     4007        4
1023523     4008        4
1023524     4009        5
1023525     4009        5
1023526     4009        6   x
1023527     4010        6
1023528     4011        6

I need to write a method to do an error check on all the table rows and ensure that any CodeNum only have one LineNum assigned to it.
eg rows with CodeNum 4002 has only LineNum 1 assigned to it, & say rows with CodeNum 4005 has only LineNum 3 assigned to it.

Its OK for a LineNum to be associated with more than one CodeNum but not a CodeNum to be associated with more than one LineNum value.

There is an error in the example above where the 3rd row with CodeNum 4009 has LineNum 6 instead of 5, here’s where I want an error message to pop up saying something like Error row id 1023526.

The real table/data contains many rows and there is no pattern to the CodeNum values and LineNum values, (all the values are integers).

I hope that makes sense.
I’m struggling to think of a quick succinct way to code this error check method.

Answer 1

You could convert to a lookup and then search for groupings with a count > 1:

using System.Linq;

var badRecords = collection.ToLookup(x => x.CodeNum).Where(y => y.Count() > 1);