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https://issues.apache.org/jira/browse/LUCENE-6595?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14595289#comment-14595289
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Cao Manh Dat commented on LUCENE-6595:
--------------------------------------
Currently CharFilter have two problems.
Problem 1:
{code}
Input : A B C ) ) )
Output : A B C
{code}
When Tokenizer ask to correct offset of 3 (which is C in output). This offset
related to offset 3 4 5 6 in the input. CharFilter will correct offset of C to
6 ( end of range ).
So why cccc -> cc have correct offset?
{code}
Input : c c c c
Output : c c
{code}
Because offset 2 (which is the second c in output) related to offset 2 3 4 in
the input. CharFilter will correct offset 2 to 4 (end of range, which is
correct).
The different of two examples, In Ex1 : the replacement happen right in the
correct point (at 3) and in Ex2 : the replacement happen before the correct
point (at 0). So I store an inputOffsets[] which is the start for each
replacements.
Problem 2:
{code}
Input : A <space> ( C
Output : A <space> C
{code}
When Tokenizer ask to correct offset of 3 (which is C in output). This offset
related to offset 3 4 in the input. CharFilter will correct offset of C to 4
(end of range, which is correct). But in this example the replacement also
happen right in the correct point. So there is a difference between correct
startOffset and endOffset.
The root of problems is we mapping N -> 1 and then asking an inverse mapping 1
-> 1.
[~dsmiley] I will look at LUCENE-5734 and try to fix that bug.
> CharFilter offsets correction is wonky
> --------------------------------------
>
> Key: LUCENE-6595
> URL: https://issues.apache.org/jira/browse/LUCENE-6595
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Michael McCandless
> Attachments: LUCENE-6595.patch
>
>
> Spinoff from this original Elasticsearch issue:
> https://github.com/elastic/elasticsearch/issues/11726
> If I make a MappingCharFilter with these mappings:
> {noformat}
> ( ->
> ) ->
> {noformat}
> i.e., just erase left and right paren, then tokenizing the string
> "(F31)" with e.g. WhitespaceTokenizer, produces a single token F31,
> with start offset 1 (good).
> But for its end offset, I would expect/want 4, but it produces 5
> today.
> This can be easily explained given how the mapping works: each time a
> mapping rule matches, we update the cumulative offset difference,
> conceptually as an array like this (it's encoded more compactly):
> {noformat}
> Output offset: 0 1 2 3
> Input offset: 1 2 3 5
> {noformat}
> When the tokenizer produces F31, it assigns it startOffset=0 and
> endOffset=3 based on the characters it sees (F, 3, 1). It then asks
> the CharFilter to correct those offsets, mapping them backwards
> through the above arrays, which creates startOffset=1 (good) and
> endOffset=5 (bad).
> At first, to fix this, I thought this is an "off-by-1" and when
> correcting the endOffset we really should return
> 1+correct(outputEndOffset-1), which would return the correct value (4)
> here.
> But that's too naive, e.g. here's another example:
> {noformat}
> cccc -> cc
> {noformat}
> If I then tokenize cccc, today we produce the correct offsets (0, 4)
> but if we do this "off-by-1" fix for endOffset, we would get the wrong
> endOffset (2).
> I'm not sure what to do here...
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