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From Damerian <>
Subject Implement a custom similarity
Date Sun, 19 Feb 2012 18:46:43 GMT
I am really new to Lucene, last week through this list i was really 
successfull into finding a solution to my problem.
I have a new question now, i am trying to implement a new similarity 
class that uses the Jaccard coefficient, i have been reading the 
javadocs and a lot of other webpages on the matter, but my problem is 
that i still cannot understand how to do it.
So far i know that i have to subclass the DefaultSimilarity and (if i am 
not wrong) i have to edit all the build in methods to return the corect 
score. Since Jaccard coefficiency is the conjuction of the 
query/document sets divided by the union of the two sets i think i only 
need the coord(q,d) and all the rest measures in the default similarity 
can return 1 to the score computation. My problem is that i cannot 
locate how to obtain the number of terms that each document has.
Also do you think this approach is correct?
I would be gratefull if you could give me advice or point towards a 
tutorial on the matter cause two days of searching were fruitless in 
finding an example code.
Thank you in advance.

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