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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 11:29:12 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13575739#comment-13575739
] 

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

bq. I just wonder if we really should restrict our TF to not fix offsets? Kind of an odd thing
though. What should a tokenfilter like this do instead?

I think that for some examples, it makes sense not to fix offsets? In the case of the URL
example ({{(https?://([a-zA-Z\-_0-9.]+))}}), I think it makes sense to highlight the whole
URL (including the leading http(s)://) even if the query term is just {{www.mysite.com}}.
On the other hand, it could be weird if the goal was to split a long CamelCase token (letsPartyLIKEits1999_dude),
but maybe this should be done by a Tokenizer rather than a TokenFilter?

(No strong feeling here, I'd just like to see if we can find a way to commit this patch without
having to grow our TokenFilter exclusion list.)
                
> 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, 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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