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https://issues.apache.org/jira/browse/LUCENE-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13575811#comment-13575811
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Clinton Gormley commented on LUCENE-4766:
-----------------------------------------
OK, so I should redo this as a tokenizer, and set positionLengths correctly.
One issue is that, because there are multiple patterns, the emitted tokens can
overlap, eg:
{code}
"foobarbaz" -> foo, foobar, oba, bar, baz
{code}
in which case I think I would need to emit:
{code}
positions: 1, 1, 2, 3, 5
position lengths: 2, 4, 2, 2, 1
start offsets: 0, 0, 0, 0, 0
end offsets: 3, 6, 3, 3, 3
{code}
Is this correct? It's starting to look quite complex...
> 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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