Grouping in BW excel report

Hi Experts,

I have a requirement, where user wants to see report based on grouping. Its like, I have various materials in the report and user wants based on high prior material ( Mat 1, 3, 5, 10) Medium Priority material ( 13,4,2,6..) Low priority material ( 7,11,9). This material grouping may be changed, over a period of time. What is the best way to implement this requirement ?And also, if these grouping can be shown in the report then, they able to drill down to check the material belonging to them

thanks in advance

D bret