how to classify the search results by an indexed field with lucene?

[Joey]

Hi all,

I use lucene as the indexer in nutch 1.2. I want to get the classified 
search results by an indexed field, for example to show the hit count 
distributions of different months in a year.

I found that in lucene 2.* this could be achieved by the 
QueryFilter().bit(IndexReader) method and calculate the hit count for 
each category. But in lucene 3.*, the class of QueryFilter has been 
removed and I couldn't find the equivalent of that method.

Could anyone tell me how to make this achievement effectively? Thanks 
very much.

Regards,
Joey