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https://issues.apache.org/jira/browse/LUCENE-7960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16461683#comment-16461683
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Robert Muir commented on LUCENE-7960:
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my biggest concern is that these filters would then have two ctors:
* NGramTokenFilter(TokenStream)
* NGramTokenFilter(TokenStream, int, int, boolean, boolean)
The no-arg one starts looking more attractive to users at this point, and its
mega-trappy (n=1,2)!!!!!!! That's the ctor that should be deprecated :)
In general I'll be honest, I don't like how trappy the apis are with these
filters/tokenizers because of defaults like that. I also think its trappy they
take a min and a max at all, because that's really creating (max-min) indexed
fields all unioned into one. There aren't even any warnings about this.
I haven't reviewed what the booleans of the patch does, but I am concerned that
the use case may just be "keep original" which could be one boolean, or perhaps
done in a different way entirely (e.g. KeywordRepeatFilter or perhaps something
like LUCENE-8273). So if its acceptable to collapse it into one boolean that
does that, I think that would be easier.
I feel like any defaults that our apis lead to (and when you have multiple
ctors, then thats a default) should be something that will perform and scale
well and work for the general case. For example n=4 has been shown to work well
in many relevance experiments. At least we should make it easy for you to
explicitly ask for something like that without passing many parameters.
> NGram filters -- add option to keep short terms
> -----------------------------------------------
>
> Key: LUCENE-7960
> URL: https://issues.apache.org/jira/browse/LUCENE-7960
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/analysis
> Reporter: Shawn Heisey
> Priority: Major
> Attachments: LUCENE-7960.patch, LUCENE-7960.patch
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> When ngram or edgengram filters are used, any terms that are shorter than the
> minGramSize are completely removed from the token stream.
> This is probably 100% what was intended, but I've seen it cause a lot of
> problems for users. I am not suggesting that the default behavior be
> changed. That would be far too disruptive to the existing user base.
> I do think there should be a new boolean option, with a name like
> keepShortTerms, that defaults to false, to allow the short terms to be
> preserved.
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