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https://issues.apache.org/jira/browse/LUCENE-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13575731#comment-13575731
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Simon Willnauer commented on LUCENE-4766:
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bq. 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).
yeah I agree offsets are tricky here. 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?
> 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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