How to return a function result instead of doclist in the Solr collapsing/grouping feature?

[Pablo Ricco]

I have the following solr fields in schema.xml:

   - id (string)
   - name (string)
   - category(string)
   - latitude (double)
   - longitude(double)

Is it possible to make a query that groups by category and returns the
average of latitude and longitude instead of the doclist?

Thanks,
Pablo