map-reduce question

["Kevin R. Coombes" <ke...@gmail.com>]

Hi,

I have a database with documents that each include two categorical and 
one continuous value.  Something like

     {
         fruit: "apple",
         size: "small",
         quality: 1.7
     },
     {
         fruit: "banana",
         size: "large",
         quality: 3.6
     }

I'd like to be able to compute responses to views/queries that basically 
ask:
     how many documents do I have (broken down by 'fruit' and 'size') 
that have the 'quality' greater than some cutoff?

And I'm having trouble identifying the appropriate couch map/reduce view 
to implement this.  If I emit keys of the form
     [doc.quality, doc.fruit, doc.size]
then I can do the quality-based searches using
     http://couch/db/_design/whatever/_view/quality?startkey=[2]
but the default "_count" kinds of reduce functions will split things up 
by quality, which I only care about for the filtering aspects.

How do I write the reduce function to skip the top level?

     Kevin