Source code
Description: source: package: org.apache.commons.text.similarity, class: FuzzyScore

    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.text.similarity;
    018
    019import java.util.Locale;
    020
    021/**
    022 * A matching algorithm that is similar to the searching algorithms implemented in editors such
    023 * as Sublime Text, TextMate, Atom and others.
    024 *
    025 * <p>
    026 * One point is given for every matched character. Subsequent matches yield two bonus points. A higher score
    027 * indicates a higher similarity.
    028 * </p>
    029 *
    030 * <p>
    031 * This code has been adapted from Apache Commons Lang 3.3.
    032 * </p>
    033 *
    034 * @since 1.0
    035 */
    036public class FuzzyScore {
    037
    038    /**
    039     * Locale used to change the case of text.
    040     */
    041    private final Locale locale;
    042
    043    /**
    044     * This returns a {@link Locale}-specific {@link FuzzyScore}.
    045     *
    046     * @param locale The string matching logic is case insensitive.
    047                     A {@link Locale} is necessary to normalize both Strings to lower case.
    048     * @throws IllegalArgumentException
    049     *         This is thrown if the {@link Locale} parameter is {@code null}.
    050     */
    051    public FuzzyScore(final Locale locale) {
    052        if (locale == null) {
    053            throw new IllegalArgumentException("Locale must not be null");
    054        }
    055        this.locale = locale;
    056    }
    057
    058    /**
    059     * Find the Fuzzy Score which indicates the similarity score between two
    060     * Strings.
    061     *
    062     * <pre>
    063     * score.fuzzyScore(null, null)                          = IllegalArgumentException
    064     * score.fuzzyScore("not null", null)                    = IllegalArgumentException
    065     * score.fuzzyScore(null, "not null")                    = IllegalArgumentException
    066     * score.fuzzyScore("", "")                              = 0
    067     * score.fuzzyScore("Workshop", "b")                     = 0
    068     * score.fuzzyScore("Room", "o")                         = 1
    069     * score.fuzzyScore("Workshop", "w")                     = 1
    070     * score.fuzzyScore("Workshop", "ws")                    = 2
    071     * score.fuzzyScore("Workshop", "wo")                    = 4
    072     * score.fuzzyScore("Apache Software Foundation", "asf") = 3
    073     * </pre>
    074     *
    075     * @param term a full term that should be matched against, must not be null
    076     * @param query the query that will be matched against a term, must not be
    077     *            null
    078     * @return result score
    079     * @throws IllegalArgumentException if the term or query is {@code null}
    080     */
    081    public Integer fuzzyScore(final CharSequence term, final CharSequence query) {
    082        if (term == null || query == null) {
    083            throw new IllegalArgumentException("CharSequences must not be null");
    084        }
    085
    086        // fuzzy logic is case insensitive. We normalize the Strings to lower
    087        // case right from the start. Turning characters to lower case
    088        // via Character.toLowerCase(char) is unfortunately insufficient
    089        // as it does not accept a locale.
    090        final String termLowerCase = term.toString().toLowerCase(locale);
    091        final String queryLowerCase = query.toString().toLowerCase(locale);
    092
    093        // the resulting score
    094        int score = 0;
    095
    096        // the position in the term which will be scanned next for potential
    097        // query character matches
    098        int termIndex = 0;
    099
    100        // index of the previously matched character in the term
    101        int previousMatchingCharacterIndex = Integer.MIN_VALUE;
    102
    103        for (int queryIndex = 0; queryIndex < queryLowerCase.length(); queryIndex++) {
    104            final char queryChar = queryLowerCase.charAt(queryIndex);
    105
    106            boolean termCharacterMatchFound = false;
    107            for (; termIndex < termLowerCase.length()
    108                    && !termCharacterMatchFound; termIndex++) {
    109                final char termChar = termLowerCase.charAt(termIndex);
    110
    111                if (queryChar == termChar) {
    112                    // simple character matches result in one point
    113                    score++;
    114
    115                    // subsequent character matches further improve
    116                    // the score.
    117                    if (previousMatchingCharacterIndex + 1 == termIndex) {
    118                        score += 2;
    119                    }
    120
    121                    previousMatchingCharacterIndex = termIndex;
    122
    123                    // we can leave the nested loop. Every character in the
    124                    // query can match at most one character in the term.
    125                    termCharacterMatchFound = true;
    126                }
    127            }
    128        }
    129
    130        return score;
    131    }
    132
    133    /**
    134     * Gets the locale.
    135     *
    136     * @return The locale
    137     */
    138    public Locale getLocale() {
    139        return locale;
    140    }
    141
    142}