Concatenate values per customer per category

Hello gurus,

The following records are retrieved via BEx query:

Customer Category     Value

11111          A               5
11111          A               6

11111          B               1

22222          A               17

22222          A               20  

22222          C               35

Output in WEBI report should be:

Customer     Cat.          Value

11111          A               5, 6

11111          B               1

22222          A               17, 20

22222          C               35

I am trying to use the Previous() function but without the desired result.

Any help highly appreciated.

regards marcel