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https://issues.apache.org/jira/browse/LUCENE-1343?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12858144#action_12858144
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Robert Muir commented on LUCENE-1343:
-------------------------------------
OK! I think we have a good solution here!.
We can use ICU's Normalizer2 to implement this, by simply creating a custom
normalization mapping.
This way we can meet multiple use-cases, e.g. someone wants to remove
diacritics, someone else doesn't.
And we get solid unicode behavior and high performance to boot.
So I will keep this issue open, I think the best solution is to take the
accent-folding mappings here (or use the ones in AsciiFoldingFilter?) and
create a .txt file of mappings, passing it to gennorm2 along with NFKC case
fold mappings.
This way we can implement this on top of LUCENE-2399, all compiled to an
efficient binary form with no code.
I'll take a shot at this once LUCENE-2399 is resolved.
> A replacement for ISOLatin1AccentFilter that does a more thorough job of
> removing diacritical marks or non-spacing modifiers.
> -----------------------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-1343
> URL: https://issues.apache.org/jira/browse/LUCENE-1343
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Analysis
> Reporter: Robert Haschart
> Priority: Minor
> Attachments: normalizer.jar, UnicodeCharUtil.java,
> UnicodeNormalizationFilter.java, UnicodeNormalizationFilterFactory.java
>
>
> The ISOLatin1AccentFilter takes Unicode characters that have diacritical
> marks and replaces them with a version of that character with the diacritical
> mark removed. For example é becomes e. However another equally valid way of
> representing an accented character in Unicode is to have the unaccented
> character followed by a non-spacing modifier character (like this: é )
> The ISOLatin1AccentFilter doesn't handle the accents in decomposed unicode
> characters at all. Additionally there are some instances where a word will
> contain what looks like an accented character, that is actually considered to
> be a separate unaccented character such as Ł but which to make searching
> easier you want to fold onto the latin1 lookalike version L .
> The UnicodeNormalizationFilter can filter out accents and diacritical marks
> whether they occur as composed characters or decomposed characters, it can
> also handle cases where as described above characters that look like they
> have diacritics (but don't) are to be folded onto the letter that they look
> like ( Ł -> L )
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