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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1448) add getFinalOffset() to TokenStream
Date Mon, 17 Nov 2008 10:20:46 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12648122#action_12648122
] 

Michael McCandless commented on LUCENE-1448:
--------------------------------------------

bq. Hmm now that we have getPositionIncrementGap() and getOffsetGap(), I think it would make
sense to also add getFinalPositionIncrement()?

We could do that.  But how would you implement it?  EG StopFilter skips tokens, and (if enabled)
already tracks the skippedPositions, so it could return that PLUS whatever its input reports
as its getFinalPositionIncrement, I guess?

bq. Could we add this as Attributes using the new API? FinalOffsetAttribute and FinalPositionIncrementAttribute?

Hmm we could do that... but it seems awkward to add new attributes that apply only to ending
state of the tokenizer.

I wonder if instead, w/ the new API, we could simply allow querying of certain attributes
(offset, posincr) after incrementToken returns "false"?

Why don't you commit the new TokenStream API first, and we can iterate on this issue &
commit 2nd?

> add getFinalOffset() to TokenStream
> -----------------------------------
>
>                 Key: LUCENE-1448
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1448
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Analysis
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: LUCENE-1448.patch, LUCENE-1448.patch, LUCENE-1448.patch, LUCENE-1448.patch
>
>
> If you add multiple Fieldable instances for the same field name to a document, and you
then index those fields with TermVectors storing offsets, it's very likely the offsets for
all but the first field instance will be wrong.
> This is because IndexWriter under the hood adds a cumulative base to the offsets of each
field instance, where that base is 1 + the endOffset of the last token it saw when analyzing
that field.
> But this logic is overly simplistic.  For example, if the WhitespaceAnalyzer is being
used, and the text being analyzed ended in 3 whitespace characters, then that information
is lost and then next field's offsets are then all 3 too small.  Similarly, if a StopFilter
appears in the chain, and the last N tokens were stop words, then the base will be 1 + the
endOffset of the last non-stopword token.
> To fix this, I'd like to add a new getFinalOffset() to TokenStream.  I'm thinking by
default it returns -1, which means "I don't know so you figure it out", meaning we fallback
to the faulty logic we have today.
> This has come up several times on the user's list.

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