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From "Grant Ingersoll (JIRA)" <>
Subject [jira] Commented: (LUCENE-1224) NGramTokenFilter creates bad TokenStream
Date Thu, 15 May 2008 10:25:55 GMT


Grant Ingersoll commented on LUCENE-1224:

OK, let me change the comment.  You can test this problem without indexing and querying. 
All of the information is available on the token.  I would suggest you revert the test to
it's original and then modify testNGrams()  by adding asserts that check that the positionIncrement
value is set properly.   By going the indexing/querying route, you are not only testing the
token filters, but pretty much all of Lucene and are thus subject to any problems there. 
In other words, it ain't a unit test.  If you set the posiitionIncrement properly and test
for it, it will work in Lucene for the queries, etc.  If it doesn't, we have much bigger problems
than ngrams.  That being said, if you want to fix testNgrams, and leave the query case in,
that is fine by me.

> NGramTokenFilter creates bad TokenStream
> ----------------------------------------
>                 Key: LUCENE-1224
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: contrib/*
>            Reporter: Hiroaki Kawai
>            Assignee: Grant Ingersoll
>            Priority: Critical
>         Attachments: LUCENE-1224.patch, NGramTokenFilter.patch, NGramTokenFilter.patch
> With current trunk NGramTokenFilter(min=2,max=4) , I index "abcdef" string into an index,
but I can't query it with "abc". If I query with "ab", I can get a hit result.
> The reason is that the NGramTokenFilter generates badly ordered TokenStream. Query is
based on the Token order in the TokenStream, that how stemming or phrase should be anlayzed
is based on the order (Token.positionIncrement).
> With current filter, query string "abc" is tokenized to : ab bc abc 
> meaning "query a string that has ab bc abc in this order".
> Expected filter will generate : ab abc(positionIncrement=0) bc
> meaning "query a string that has (ab|abc) bc in this order"
> I'd like to submit a patch for this issue. :-)

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