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From "Adrien Grand (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4766) Pattern token filter which emits a token for every capturing group
Date Mon, 11 Feb 2013 10:23:13 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13575718#comment-13575718
] 

Adrien Grand commented on LUCENE-4766:
--------------------------------------

bq. I like that all patterns operate on the same CharSequence and that you are setting offsets
right.

Does this filter need to set offsets? I'm worried that under certain circumstances filters
that modify offsets might create inconsistent offset graphs (because they don't know what
filters have been applied before, there is an exclusion list for filters that modify offsets
in TestRandomChains).
                
> Pattern token filter which emits a token for every capturing group
> ------------------------------------------------------------------
>
>                 Key: LUCENE-4766
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4766
>             Project: Lucene - Core
>          Issue Type: New Feature
>          Components: modules/analysis
>    Affects Versions: 4.1
>            Reporter: Clinton Gormley
>            Assignee: Simon Willnauer
>            Priority: Minor
>              Labels: analysis, feature, lucene
>             Fix For: 4.2
>
>         Attachments: LUCENE-4766.patch
>
>
> The PatternTokenizer either functions by splitting on matches, or allows you to specify
a single capture group.  This is insufficient for my needs. Quite often I want to capture
multiple overlapping tokens in the same position.
> I've written a pattern token filter which accepts multiple patterns and emits tokens
for every capturing group that is matched in any pattern.
> Patterns are not anchored to the beginning and end of the string, so each pattern can
produce multiple matches.
> For instance a pattern like :
> {code}
>     "(([a-z]+)(\d*))"
> {code}
> when matched against: 
> {code}
>     "abc123def456"
> {code}
> would produce the tokens:
> {code}
>     abc123, abc, 123, def456, def, 456
> {code}
> Multiple patterns can be applied, eg these patterns could be used for camelCase analysis:
> {code}
>     "([A-Z]{2,})",
>     "(?<![A-Z])([A-Z][a-z]+)",
>     "(?:^|\\b|(?<=[0-9_])|(?<=[A-Z]{2}))([a-z]+)",
>     "([0-9]+)"
> {code}
> When matched against the string "letsPartyLIKEits1999_dude", they would produce the tokens:
> {code}
>     lets, Party, LIKE, its, 1999, dude
> {code}
> If no token is emitted, the original token is preserved. 
> If the preserveOriginal flag is true, it will output the full original token (ie "letsPartyLIKEits1999_dude")
in addition to any matching tokens (but in this case, if a matching token is identical to
the original, it will only emit one copy of the full token).
> Multiple patterns are required to allow overlapping captures, but also means that patterns
are less dense and easier to understand.
> This is my first Java code, so apologies if I'm doing something stupid.

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