1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.text.similarity;
18
19 import java.util.HashSet;
20 import java.util.Set;
21
22 /**
23 * Measures the Jaccard similarity (aka Jaccard index) of two sets of character
24 * sequence. Jaccard similarity is the size of the intersection divided by the
25 * size of the union of the two sets.
26 *
27 * <p>
28 * For further explanation about Jaccard Similarity, refer
29 * https://en.wikipedia.org/wiki/Jaccard_index
30 * </p>
31 *
32 * @since 1.0
33 */
34 public class JaccardSimilarity implements SimilarityScore<Double> {
35
36 /**
37 * Singleton instance.
38 */
39 static final JaccardSimilarity INSTANCE = new JaccardSimilarity();
40
41 /**
42 * Calculates Jaccard Similarity of two set character sequence passed as
43 * input.
44 *
45 * @param left first character sequence
46 * @param right second character sequence
47 * @return index
48 * @throws IllegalArgumentException
49 * if either String input {@code null}
50 */
51 @Override
52 public Double apply(final CharSequence left, final CharSequence right) {
53 if (left == null || right == null) {
54 throw new IllegalArgumentException("Input cannot be null");
55 }
56 return calculateJaccardSimilarity(left, right);
57 }
58
59 /**
60 * Calculates Jaccard Similarity of two character sequences passed as
61 * input. Does the calculation by identifying the union (characters in at
62 * least one of the two sets) of the two sets and intersection (characters
63 * which are present in set one which are present in set two)
64 *
65 * @param left first character sequence
66 * @param right second character sequence
67 * @return index
68 */
69 private Double calculateJaccardSimilarity(final CharSequence left, final CharSequence right) {
70 final int leftLength = left.length();
71 final int rightLength = right.length();
72 if (leftLength == 0 && rightLength == 0) {
73 return 1d;
74 }
75 if (leftLength == 0 || rightLength == 0) {
76 return 0d;
77 }
78 final Set<Character> leftSet = new HashSet<>();
79 for (int i = 0; i < leftLength; i++) {
80 leftSet.add(left.charAt(i));
81 }
82 final Set<Character> rightSet = new HashSet<>();
83 for (int i = 0; i < rightLength; i++) {
84 rightSet.add(right.charAt(i));
85 }
86 final Set<Character> unionSet = new HashSet<>(leftSet);
87 unionSet.addAll(rightSet);
88 final int intersectionSize = leftSet.size() + rightSet.size() - unionSet.size();
89 return 1.0d * intersectionSize / unionSet.size();
90 }
91 }