Serial number with conditions

[kauser]

Hello, 

how can i add a serial number with some conditions - 

Input Data 

F1	F2
AB	1234
AB	1234
AB	1234
AB	1234
CD	5678
CD	5678
CD	5678
CD	5678
CD	5678
CD	5678
EF	6987
EF	6987

Expected Output (with serial column) 

F1	F2	Serial
AB	1234	4
AB	1234	4
AB	1234	4
AB	1234	4
CD	5678	8
CD	5678	8
CD	5678	8
CD	5678	8
CD	5678	8
CD	5678	8
EF	6987	10
EF	6987	10

[BS_THE_ANALYST]

Could you provide the logic how you go from the input data to generate the serial column? It's difficult to advise otherwise.

All the best,

BS

[Qiu · Accepted solution]

@kauser 
I can either understand how the logic of your Serial Number, but normally we can use Tile Tool to generate the Serial Number per groups.