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* Copyright 2004 The Apache Software Foundation.
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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package org.apache.lucene.search.similar;
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import java.io.IOException;
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import java.io.StringReader;
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import java.util.HashSet;
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import org.apache.lucene.analysis.Analyzer;
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import org.apache.lucene.analysis.TokenStream;
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import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
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import org.apache.lucene.index.Term;
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import org.apache.lucene.search.BooleanClause;
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import org.apache.lucene.search.BooleanQuery;
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import org.apache.lucene.search.IndexSearcher;
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import org.apache.lucene.search.Query;
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import org.apache.lucene.search.TermQuery;
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* Simple similarity measures.
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public final class SimilarityQueries
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private SimilarityQueries()
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* Simple similarity query generators.
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* Takes every unique word and forms a boolean query where all words are optional.
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* After you get this you'll use to to query your {@link IndexSearcher} for similar docs.
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* The only caveat is the first hit returned <b>should be</b> your source document - you'll
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* need to then ignore that.
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* So, if you have a code fragment like this:
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* Query q = formSimilaryQuery( "I use Lucene to search fast. Fast searchers are good", new StandardAnalyzer(), "contents", null);
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* The query returned, in string form, will be <code>'(i use lucene to search fast searchers are good')</code>.
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* The philosophy behind this method is "two documents are similar if they share lots of words".
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* Note that behind the scenes, Lucene's scoring algorithm will tend to give two documents a higher similarity score if the share more uncommon words.
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* This method is fail-safe in that if a long 'body' is passed in and
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* {@link BooleanQuery#add BooleanQuery.add()} (used internally)
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* {@link org.apache.lucene.search.BooleanQuery.TooManyClauses BooleanQuery.TooManyClauses}, the
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* query as it is will be returned.
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* @param body the body of the document you want to find similar documents to
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* @param a the analyzer to use to parse the body
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* @param field the field you want to search on, probably something like "contents" or "body"
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* @param stop optional set of stop words to ignore
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* @return a query with all unique words in 'body'
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* @throws IOException this can't happen...
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public static Query formSimilarQuery( String body,
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TokenStream ts = a.reusableTokenStream( field, new StringReader( body));
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CharTermAttribute termAtt = ts.addAttribute(CharTermAttribute.class);
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BooleanQuery tmp = new BooleanQuery();
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Set<String> already = new HashSet<String>(); // ignore dups
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while (ts.incrementToken()) {
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String word = termAtt.toString();
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// ignore opt stop words
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stop.contains( word)) continue;
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if ( ! already.add( word)) continue;
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TermQuery tq = new TermQuery( new Term( field, word));
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tmp.add( tq, BooleanClause.Occur.SHOULD);
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catch( BooleanQuery.TooManyClauses too)
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// fail-safe, just return what we have, not the end of the world