not quite a cross tab query...

Hello pgsql listers,

I've got a problem that is similar to, but I don't think identical to,
a cross tab query. My data looks like:
  ID | CAT
  1  |   A
  1  |   B
  2  |   A
  2  |   C
So for each ID there may be many CAT (categories).
The client wants it to look like:
  ID | CATS
  1  |  A,B
  2  |  A,C
Where each ID is unique in the results, and the CAT values are
concatenated with a comma separator.

There are about 100 unique CAT values. They only way I can see to do
it is programatically with a for loop. But before I do that I wanted
to bounce it off the fine minds that inhabit this list.

Thanks,
Rich

-- 
Richard Greenwood
richard.greenwood@gmail.com
www.greenwoodmap.com