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From "Adrien Grand (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (LUCENE-2947) NGramTokenizer shouldn't trim whitespace
Date Fri, 26 Apr 2013 22:18:17 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-2947?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Adrien Grand resolved LUCENE-2947.
----------------------------------

    Resolution: Fixed

NGramTokenizer doesn't trim whitespaces anymore (LUCENE-4955).
                
> NGramTokenizer shouldn't trim whitespace
> ----------------------------------------
>
>                 Key: LUCENE-2947
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2947
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: modules/analysis
>    Affects Versions: 3.0.3
>            Reporter: David Byrne
>            Priority: Minor
>         Attachments: LUCENE-2947.patch, NGramTokenizerTest.java
>
>
> Before I tokenize my strings, I am padding them with white space:
> String foobar = " " + foo + " " + bar + " ";
> When constructing term vectors from ngrams, this strategy has a couple benefits.  First,
it places special emphasis on the starting and ending of a word.  Second, it improves the
similarity between phrases with swapped words.  " foo bar " matches " bar foo " more closely
than "foo bar" matches "bar foo".
> The problem is that Lucene's NGramTokenizer trims whitespace.  This forces me to do some
preprocessing on my strings before I can tokenize them:
> foobar.replaceAll(" ","$"); //arbitrary char not in my data
> This is undocumented, so users won't realize their strings are being trim()'ed, unless
they look through the source, or examine the tokens manually.
> I am proposing NGramTokenizer should be changed to respect whitespace.  Is there a compelling
reason against this?

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