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From "Hiroaki Kawai (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1224) NGramTokenFilter creates bad TokenStream
Date Thu, 15 May 2008 11:45:56 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12597098#action_12597098
] 

Hiroaki Kawai commented on LUCENE-1224:
---------------------------------------

In my understanding,
----------
The sequence we have "This is an example"

If we want to tokenize with white space tokenizer, the tokens are
"This", "is", "an", "example"
positions are 0,1,2,3

If we want to tokenize with 2-gram, the tokens are
"Th" "hi" "is" "s " " i" "is" "s " " a" "an" "n " " e" "ex" "xa" "am" "mp" "pl" "le"
positions are 0,1,2,3,4,...


> NGramTokenFilter creates bad TokenStream
> ----------------------------------------
>
>                 Key: LUCENE-1224
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1224
>             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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