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From "Chris Harris (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-1370) Patch to make ShingleFilter output a unigram if no ngrams can be generated
Date Fri, 29 Aug 2008 22:57:44 GMT
Patch to make ShingleFilter output a unigram if no ngrams can be generated
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                 Key: LUCENE-1370
                 URL: https://issues.apache.org/jira/browse/LUCENE-1370
             Project: Lucene - Java
          Issue Type: Improvement
          Components: contrib/analyzers
            Reporter: Chris Harris
         Attachments: ShingleFilter.patch

Currently if ShingleFilter.outputUnigrams==false and the underlying token stream is only one
token long, then ShingleFilter.next() won't return any tokens. This patch provides a new option,
outputUnigramIfNoNgrams; if this option is set and the underlying stream is only one token
long, then ShingleFilter will return that token, regardless of the setting of outputUnigrams.

My use case here is speeding up phrase queries. The technique is as follows:

First, doing index-time analysis using ShingleFilter (using outputUnigrams==true), thereby
expanding things as follows:

"please divide this sentence into shingles" ->
 "please", "please divide"
 "divide", "divide this"
 "this", "this sentence"
 "sentence", "sentence into"
 "into", "into shingles"
 "shingles"

Second, do query-time analysis using ShingleFilter (using outputUnigrams==false and outputUnigramIfNoNgrams==true).
If the user enters a phrase query, it will get tokenized in the following manner:

"please divide this sentence into shingles" ->
 "please divide"
 "divide this"
 "this sentence"
 "sentence into"
 "into shingles"

By doing phrase queries with bigrams like this, I can gain a very considerable speedup. Without
the outputUnigramIfNoNgrams option, then a single word query would tokenize like this:

"please" ->
   [no tokens]

But thanks to outputUnigramIfNoNgrams, single words will now tokenize like this:

"please" ->
  "please"

****

The patch also adds a little to the pre-outputUnigramIfNoNgrams option tests.

****

I'm not sure if the patch in this state is useful to anyone else, but I thought I should throw
it up here and try to find out.


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