updating internal table in loop

Hi All,

UID  GRP1  GRP2 UPD1

001     1         1     1

001    1          2     2

001    1          3     3

001    2          4     1

002    1         3      1

002    1         2      2

003    1         4      1

004    1        1      1

004    2        2      1

004    2        5       2

I have a requirement where I have an internal table it_data with four fields UID, GRP1, GRP2 and UPD1

so now the requirement is based on UID and GRP1 the UPD1 field will be updated, so for same UID and for the same GRP1 all the UPD1 will be incremented like 1, 2, 3 and so on..

so in the above example, for UID 001 and GRP1 1 the UPD1 is updated as 1

then for the same UID and the same GRP 1 i.e. 1 the UPD1 will be incremented to 2 and so on.

then for the same UID but for the different/new GRP1 the UPD field will start from 1 again and so on.

I am not able to write the loop statement for this req.