org.apache.lucene.search.spell.HighFrequencyDictionary.java Source code

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Here is the source code for org.apache.lucene.search.spell.HighFrequencyDictionary.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.apache.lucene.search.spell;

import java.io.IOException;
import java.util.Set;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.MultiTerms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.index.Terms;
import org.apache.lucene.search.suggest.InputIterator;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;

/**
 * HighFrequencyDictionary: terms taken from the given field
 * of a Lucene index, which appear in a number of documents
 * above a given threshold.
 *
 * Threshold is a value in [0..1] representing the minimum
 * number of documents (of the total) where a term should appear.
 * 
 * Based on LuceneDictionary.
 */
public class HighFrequencyDictionary implements Dictionary {
    private IndexReader reader;
    private String field;
    private float thresh;

    /**
     * Creates a new Dictionary, pulling source terms from
     * the specified <code>field</code> in the provided <code>reader</code>.
     * <p>
     * Terms appearing in less than <code>thresh</code> percentage of documents
     * will be excluded.
     */
    public HighFrequencyDictionary(IndexReader reader, String field, float thresh) {
        this.reader = reader;
        this.field = field;
        this.thresh = thresh;
    }

    @Override
    public final InputIterator getEntryIterator() throws IOException {
        return new HighFrequencyIterator();
    }

    final class HighFrequencyIterator implements InputIterator {
        private final BytesRefBuilder spare = new BytesRefBuilder();
        private final TermsEnum termsEnum;
        private int minNumDocs;
        private long freq;

        HighFrequencyIterator() throws IOException {
            Terms terms = MultiTerms.getTerms(reader, field);
            if (terms != null) {
                termsEnum = terms.iterator();
            } else {
                termsEnum = null;
            }
            minNumDocs = (int) (thresh * (float) reader.numDocs());
        }

        private boolean isFrequent(int freq) {
            return freq >= minNumDocs;
        }

        @Override
        public long weight() {
            return freq;
        }

        @Override
        public BytesRef next() throws IOException {
            if (termsEnum != null) {
                BytesRef next;
                while ((next = termsEnum.next()) != null) {
                    if (isFrequent(termsEnum.docFreq())) {
                        freq = termsEnum.docFreq();
                        spare.copyBytes(next);
                        return spare.get();
                    }
                }
            }
            return null;
        }

        @Override
        public BytesRef payload() {
            return null;
        }

        @Override
        public boolean hasPayloads() {
            return false;
        }

        @Override
        public Set<BytesRef> contexts() {
            return null;
        }

        @Override
        public boolean hasContexts() {
            return false;
        }
    }
}