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

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Here is the source code for org.apache.lucene.search.spell.JaroWinklerDistance.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.util.Arrays;

/**
 * Similarity measure for short strings such as person names.
 * <p>
 * @see <a href="http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance">http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance</a>
 */
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 + ")";
    }

}