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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch licenses this file to you under
* the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.elasticsearch.search.suggest.phrase;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Terms;
import org.apache.lucene.util.BytesRef;
import org.elasticsearch.search.suggest.SuggestUtils;
import org.elasticsearch.search.suggest.phrase.DirectCandidateGenerator.Candidate;
import java.io.IOException;
public class StupidBackoffScorer extends WordScorer {
public static final WordScorerFactory FACTORY = new WordScorer.WordScorerFactory() {
@Override
public WordScorer newScorer(IndexReader reader, Terms terms, String field, double realWordLikelyhood, BytesRef separator) throws IOException {
return new StupidBackoffScorer(reader, terms, field, realWordLikelyhood, separator, 0.4f);
}
};
private final double discount;
public StupidBackoffScorer(IndexReader reader, Terms terms,String field, double realWordLikelyhood, BytesRef separator, double discount)
throws IOException {
super(reader, terms, field, realWordLikelyhood, separator);
this.discount = discount;
}
@Override
protected double scoreBigram(Candidate word, Candidate w_1) throws IOException {
SuggestUtils.join(separator, spare, w_1.term, word.term);
final long count = frequency(spare.get());
if (count < 1) {
return discount * scoreUnigram(word);
}
return count / (w_1.frequency + 0.00000000001d);
}
@Override
protected double scoreTrigram(Candidate w, Candidate w_1, Candidate w_2) throws IOException {
// First see if there are bigrams. If there aren't then skip looking up the trigram. This saves lookups
// when the bigrams and trigrams are rare and we need both anyway.
SuggestUtils.join(separator, spare, w_1.term, w.term);
long bigramCount = frequency(spare.get());
if (bigramCount < 1) {
return discount * scoreUnigram(w);
}
SuggestUtils.join(separator, spare, w_2.term, w_1.term, w.term);
long trigramCount = frequency(spare.get());
if (trigramCount < 1) {
return discount * (bigramCount / (w_1.frequency + 0.00000000001d));
}
return trigramCount / (bigramCount + 0.00000000001d);
}
}
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