    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.Map;
    020
    021/**
    022 * Measures the cosine distance between two character sequences.
    023 *
    024 * <p>It utilizes the {@link CosineSimilarity} to compute the distance. Character sequences
    025 * are converted into vectors through a simple tokenizer that works with a regular expression
    026 * to split words in a sentence.</p>
    027 *
    028 * <p>
    029 * For further explanation about Cosine Similarity and Cosine Distance, refer to
    030 * http://en.wikipedia.org/wiki/Cosine_similarity.
    031 * </p>
    032 *
    033 * @since 1.0
    034 * @see CosineSimilarity
    035 */
    036public class CosineDistance implements EditDistance<Double> {
    037    /**
    038     * Tokenizer used to convert the character sequence into a vector.
    039     */
    040    private final Tokenizer<CharSequence> tokenizer = new RegexTokenizer();
    041    /**
    042     * Cosine similarity.
    043     */
    044    private final CosineSimilarity cosineSimilarity = new CosineSimilarity();
    045
    046    @Override
    047    public Double apply(final CharSequence left, final CharSequence right) {
    048        final CharSequence[] leftTokens = tokenizer.tokenize(left);
    049        final CharSequence[] rightTokens = tokenizer.tokenize(right);
    050
    051        final Map<CharSequence, Integer> leftVector = Counter.of(leftTokens);
    052        final Map<CharSequence, Integer> rightVector = Counter.of(rightTokens);
    053        final double similarity = cosineSimilarity.cosineSimilarity(leftVector, rightVector);
    054        return 1.0 - similarity;
    055    }
    056
    057}