| /* |
| * 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.commons.text.similarity; |
| |
| import java.util.HashSet; |
| import java.util.Set; |
| |
| /** |
| * Measures the Jaccard similarity (aka Jaccard index) of two sets of character |
| * sequence. Jaccard similarity is the size of the intersection divided by the |
| * size of the union of the two sets. |
| * |
| * <p> |
| * For further explanation about Jaccard Similarity, refer |
| * https://en.wikipedia.org/wiki/Jaccard_index |
| * </p> |
| * |
| * @since 1.0 |
| */ |
| public class JaccardSimilarity implements SimilarityScore<Double> { |
| |
| /** |
| * Calculates Jaccard Similarity of two set character sequence passed as |
| * input. |
| * |
| * @param left first character sequence |
| * @param right second character sequence |
| * @return index |
| * @throws IllegalArgumentException |
| * if either String input {@code null} |
| */ |
| @Override |
| public Double apply(final CharSequence left, final CharSequence right) { |
| if (left == null || right == null) { |
| throw new IllegalArgumentException("Input cannot be null"); |
| } |
| return calculateJaccardSimilarity(left, right); |
| } |
| |
| /** |
| * Calculates Jaccard Similarity of two character sequences passed as |
| * input. Does the calculation by identifying the union (characters in at |
| * least one of the two sets) of the two sets and intersection (characters |
| * which are present in set one which are present in set two) |
| * |
| * @param left first character sequence |
| * @param right second character sequence |
| * @return index |
| */ |
| private Double calculateJaccardSimilarity(final CharSequence left, final CharSequence right) { |
| final int leftLength = left.length(); |
| final int rightLength = right.length(); |
| if (leftLength == 0 && rightLength == 0) { |
| return 1d; |
| } |
| if (leftLength == 0 || rightLength == 0) { |
| return 0d; |
| } |
| final Set<Character> leftSet = new HashSet<>(); |
| for (int i = 0; i < leftLength; i++) { |
| leftSet.add(left.charAt(i)); |
| } |
| final Set<Character> rightSet = new HashSet<>(); |
| for (int i = 0; i < rightLength; i++) { |
| rightSet.add(right.charAt(i)); |
| } |
| final Set<Character> unionSet = new HashSet<>(leftSet); |
| unionSet.addAll(rightSet); |
| final int intersectionSize = leftSet.size() + rightSet.size() - unionSet.size(); |
| return 1.0d * intersectionSize / unionSet.size(); |
| } |
| } |