: >I have indexed a field that describes the "category" of the document.
: >Thus, I want to know how many categories have a specific term. Could
: >someone help me to get this with good performance?
I think I'm reading this question different than Chuck, so I'll toss out
somethign totally different...
as I understand it, you've indexed a bunch of documents, with a variety of
fields, one of which is "category" (for example, maybe you are indexing
news articles, that each have a "title", "description", "url", and
"category"). Now you have a term like "title:lucene" (or
"description:pope") and you want to know the number of unique terms in the
category field that exist in articles that contain your input term.
If that's what you're looking for, then you can problem achieve this by:
1) make a TermQuery for your input term (ie: "title:lucene")
2) put that TermQuery in a QueryFilter, and call bits(reader)
3) call FieldCache.DEFAULT.getStrings(reader,"category")
3) loop over the true bits in the BitSet from #3, and for each one, add
the corrisponding entry from the String[] in #4 to a Set.
when you're all done, the Set will be the list of categories, and the size
of that Set is the number (i think) you wanted.
(DISCLAIMER: I've never acctaully used FieldCache, i'm just giving you my
advice based on reading the javadocs)
-Hoss
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