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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 13:37:13 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13575786#comment-13575786
] 

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

bq. Is it OK for a tokenizer to create multiple tokens in the same positions but with different
offsets?

Although it's not common, it is perfectly fine for a Tokenizer to generate multiple tokens
in the same position.

However, I think the correct way to tokenize your example would be:
{code}
tokens: foo, foobar, bar
positions: 1, 1, 2
position lengths: 1, 2, 1
start offsets: 0, 0, 3
end offsets: 3, 6, 6
{code}

I'm not sure WordDelimiterFilter is the best example to look at. I'm not familiar with it
at all, but it's currently in the exclusion list for both positions and offsets (and is the
culprit for SOLR-4137).
                
> 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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