org.apache.lucene.search.spell.JaroWinklerDistance Maven / Gradle / Ivy
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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;
/**
* Similarity measure for short strings such as person names.
*
* @see http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance
*/
public class JaroWinklerDistance implements StringDistance {
private float threshold = 0.7f;
/**
* Creates a new distance metric with the default threshold
* for the Jaro Winkler bonus (0.7)
* @see #setThreshold(float)
*/
public JaroWinklerDistance() {}
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() };
}
@Override
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;
}
@Override
public int hashCode() {
return 113 * Float.floatToIntBits(threshold) * getClass().hashCode();
}
@Override
public boolean equals(Object obj) {
if (this == obj) return true;
if (null == obj || getClass() != obj.getClass()) return false;
JaroWinklerDistance o = (JaroWinklerDistance)obj;
return (Float.floatToIntBits(o.threshold)
== Float.floatToIntBits(this.threshold));
}
@Override
public String toString() {
return "jarowinkler(" + threshold + ")";
}
}