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Lucene example source code file (HighFrequencyDictionary.java)

This example Lucene source code file (HighFrequencyDictionary.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

highfrequencydictionary, highfrequencyiterator, highfrequencyiterator, indexreader, io, ioexception, ioexception, iterator, runtimeexception, runtimeexception, string, string, term, termenum, unsupportedoperationexception, util

The Lucene HighFrequencyDictionary.java source code

/**
 * 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.Iterator;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.search.spell.Dictionary;
import org.apache.lucene.util.StringHelper;

/**
 * HighFrequencyDictionary: terms taken from the given field
 * of a Lucene index, which appear in a number of documents
 * above a given threshold.
 *
 * When using IndexReader.terms(Term) the code must not call next() on TermEnum
 * as the first call to TermEnum, see: http://issues.apache.org/jira/browse/LUCENE-6
 *
 * 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;

  public HighFrequencyDictionary(IndexReader reader, String field, float thresh) {
    this.reader = reader;
    this.field = StringHelper.intern(field);
    this.thresh = thresh;
  }

  public final Iterator<String> getWordsIterator() {
    return new HighFrequencyIterator();
  }

  final class HighFrequencyIterator implements TermFreqIterator {
    private TermEnum termEnum;
    private Term actualTerm;
    private int actualFreq;
    private boolean hasNextCalled;
    private int minNumDocs;

    HighFrequencyIterator() {
      try {
        termEnum = reader.terms(new Term(field, ""));
        minNumDocs = (int)(thresh * (float)reader.numDocs());
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }

    private boolean isFrequent(Term term) {
      try {
        return reader.docFreq(term) >= minNumDocs;
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }

    public String next() {
      if (!hasNextCalled) {
        hasNext();
      }
      hasNextCalled = false;

      try {
        termEnum.next();
      } catch (IOException e) {
        throw new RuntimeException(e);
      }

      return (actualTerm != null) ? actualTerm.text() : null;
    }

    public float freq() {
      return actualFreq;
    }


    public boolean hasNext() {
      if (hasNextCalled) {
        return actualTerm != null;
      }
      hasNextCalled = true;

      do {
        actualTerm = termEnum.term();
        actualFreq = termEnum.docFreq();

        // if there are no words return false
        if (actualTerm == null) {
          return false;
        }

        String currentField = actualTerm.field();

        // if the next word doesn't have the same field return false
        if (currentField != field) {   // intern'd comparison
          actualTerm = null;
          return false;
        }

        // got a valid term, does it pass the threshold?
        if (isFrequent(actualTerm)) {
          return true;
        }

        // term not up to threshold
        try {
          termEnum.next();
        } catch (IOException e) {
          throw new RuntimeException(e);
        }

      } while (true);
    }

    public void remove() {
      throw new UnsupportedOperationException();
    }
  }
}

Other Lucene examples (source code examples)

Here is a short list of links related to this Lucene HighFrequencyDictionary.java source code file:

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