I implement a faceted search using Lucene. I have an index of documents and an index of a taxonomy. Then I collect facets for a given level of the taxonomy.
My question is: How can I get the number of documents indexed in a given Category of the Taxonomy?
I think that my question is quite simple but I couldn't find any method in the Lucene's API nor searching in Google. I only found how to get the number of documents in the whole index using the numDocs() method of the IndexReader class.
If you have one term for each category in the index, perhaps you can use something like TermEnum.docFreq()? You can get the TermEnum object from IndexReader.terms(Term).
I don't really know enough about your index structure to suggest the correct query for you, but if you execute a query searching for all the documents in your category, then the returned set of results will generally have a count of the total number of hits for the query.
For instance, if you query using either of:
search(Query query, int n)
search(Query query, Filter filter, int n)
Then you will get a TopDocs object back, from which you can get the total number of hits back from: TopDocs.totalHits.
