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https://issues.apache.org/jira/browse/LUCENE-4955?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13640657#comment-13640657
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Jack Krupansky commented on LUCENE-4955:
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I think that ngram filter and edge-ngram filter are rather different cases.
With edge-ngram it is abundantly clear that all of the edge ngrams "stack up"
at the same position (at least for "front" edge ngrams!). But embedded ngrams
seem more like a stretching out of the token, from one token to a sequence of
tokens. Actually, it is k overlayed sequences, where k = maxGramSize minus
minGramSize plus 1.
I think the solution should be to have a "mode" which indicates whether the
"intent" is merely variations (sub-tokens) for the token at the same position
vs. a stretching the token into a sequence of tokens. Maybe call it
"expansionMode": "stack" vs. "sequence".
But even for the latter, I would definitely recommend that each of the k
sequences should restart the position at the original token position.
> NGramTokenFilter increments positions for each gram
> ---------------------------------------------------
>
> Key: LUCENE-4955
> URL: https://issues.apache.org/jira/browse/LUCENE-4955
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/analysis
> Affects Versions: 4.3
> Reporter: Simon Willnauer
> Fix For: 5.0, 4.4
>
> Attachments: highlighter-test.patch, LUCENE-4955.patch
>
>
> NGramTokenFilter increments positions for each gram rather for the actual
> token which can lead to rather funny problems especially with highlighting.
> if this filter should be used for highlighting is a different story but today
> this seems to be a common practice in many situations to highlight sub-term
> matches.
> I have a test for highlighting that uses ngram failing with a StringIOOB
> since tokens are sorted by position which causes offsets to be mixed up due
> to ngram token filter.
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