[Zope] Zcatalog question

I have a Zcatalog setup to handle bunches of small xml files that are being stored as DTML Documents. When I do a query I would like to make the results unique on a fieldindex that is called ad_num. Is there a way to filter the results of a query to be unique on a fieldindex. I realize I can step through the results and filter out the duplicates but is there a more optimal way of doing this. I tried messing with something like this: context.Catalog({ 'adTextidx' : adTextidx}).uniqueValuesFor('ad_num') but this unfortunatly does not work. thanks for any help with this. -- Steve Lenti Systems Analyst Good night to spend with family, but avoid arguments with your mate's new lover.