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From "Kainth, Sachin" <>
Subject RE: categorisation
Date Fri, 09 Feb 2007 10:40:30 GMT
It makes sense to me only if you tell me that all the bits in the BitSet
"all" will be 1. 

-----Original Message-----
From: Erik Hatcher [] 
Sent: 08 February 2007 18:37
Subject: Re: categorisation

On Feb 8, 2007, at 12:36 PM, Kainth, Sachin wrote:

> Chris has given an example of how to perform categorisation of lucene 
> searches:
> String[] mfgs = ...;
>   String query = "+category:cameras +price:[0 to 10]";
>   Query q = QueryParser.parse(query);
>   Hits results =, mySort)
>   BitSet all = (new QueryFilter(q)).bits(reader)
>   int[] mfg_counts = new int[mfgs.length];
>   for i in (0 to mfgs.length) {
>      BitSet these = (new QueryFilter(new TermQuery("mfg",mfgs 
> [i]))).bits(reader);
>      these.and(all)
>      mfg_counts[i] = these.cardinality();
>   }
> What I don't understand though is what this line does:
> BitSet all = (new QueryFilter(q)).bits(reader)
> Anyone have any ideas?

"all" is a BitSet lit up for the documents that matched "query".   
"these" (the BitSet for a particular category) is .anded with "all"  
to get the counts _left over_ for each category given "query".

Make sense?


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