Lucene example source code file (JaroWinklerDistance.java)

This example Lucene source code file (JaroWinklerDistance.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

jarowinklerdistance, jarowinklerdistance, string, string, stringdistance, stringdistance, util

The Lucene JaroWinklerDistance.java source code

package org.apache.lucene.search.spell;

/**
 * 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.
 */

import java.util.Arrays;

public class JaroWinklerDistance implements StringDistance {

  private float threshold = 0.7f;

  private int[] matches(String s1, String s2) {
    String max, min;
    if (s1.length() > s2.length()) {
      max = s1;
      min = s2;
    } else {
      max = s2;
      min = s1;
    }
    int range = Math.max(max.length() / 2 - 1, 0);
    int[] matchIndexes = new int[min.length()];
    Arrays.fill(matchIndexes, -1);
    boolean[] matchFlags = new boolean[max.length()];
    int matches = 0;
    for (int mi = 0; mi < min.length(); mi++) {
      char c1 = min.charAt(mi);
      for (int xi = Math.max(mi - range, 0), xn = Math.min(mi + range + 1, max
          .length()); xi < xn; xi++) {
        if (!matchFlags[xi] && c1 == max.charAt(xi)) {
          matchIndexes[mi] = xi;
          matchFlags[xi] = true;
          matches++;
          break;
        }
      }
    }
    char[] ms1 = new char[matches];
    char[] ms2 = new char[matches];
    for (int i = 0, si = 0; i < min.length(); i++) {
      if (matchIndexes[i] != -1) {
        ms1[si] = min.charAt(i);
        si++;
      }
    }
    for (int i = 0, si = 0; i < max.length(); i++) {
      if (matchFlags[i]) {
        ms2[si] = max.charAt(i);
        si++;
      }
    }
    int transpositions = 0;
    for (int mi = 0; mi < ms1.length; mi++) {
      if (ms1[mi] != ms2[mi]) {
        transpositions++;
      }
    }
    int prefix = 0;
    for (int mi = 0; mi < min.length(); mi++) {
      if (s1.charAt(mi) == s2.charAt(mi)) {
        prefix++;
      } else {
        break;
      }
    }
    return new int[] { matches, transpositions / 2, prefix, max.length() };
  }

  public float getDistance(String s1, String s2) {
    int[] mtp = matches(s1, s2);
    float m = mtp[0];
    if (m == 0) {
      return 0f;
    }
    float j = ((m / s1.length() + m / s2.length() + (m - mtp[1]) / m)) / 3;
    float jw = j < getThreshold() ? j : j + Math.min(0.1f, 1f / mtp[3]) * mtp[2]
        * (1 - j);
    return jw;
  }

  /**
   * Sets the threshold used to determine when Winkler bonus should be used.
   * Set to a negative value to get the Jaro distance.
   * @param threshold the new value of the threshold
   */
  public void setThreshold(float threshold) {
    this.threshold = threshold;
  }

  /**
   * Returns the current value of the threshold used for adding the Winkler bonus.
   * The default value is 0.7.
   * @return the current value of the threshold
   */
  public float getThreshold() {
    return threshold;
  }
}