JaccardSimilarity.java
- /*
- * 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> {
- /**
- * Singleton instance.
- */
- static final JaccardSimilarity INSTANCE = new JaccardSimilarity();
- /**
- * Creates a new instance.
- */
- public JaccardSimilarity() {
- // empty
- }
- /**
- * Computes the Jaccard Similarity of two set character sequence passed as input.
- *
- * @param left first input sequence.
- * @param right second input sequence.
- * @return index.
- * @throws IllegalArgumentException if either String input {@code null}.
- */
- @Override
- public Double apply(final CharSequence left, final CharSequence right) {
- return apply(SimilarityInput.input(left), SimilarityInput.input(right));
- }
- /**
- * Computes the 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 <E> The type of similarity score unit.
- * @param left first input sequence.
- * @param right second input sequence.
- * @return index.
- * @since 1.13.0
- */
- public <E> Double apply(final SimilarityInput<E> left, final SimilarityInput<E> right) {
- if (left == null || right == null) {
- throw new IllegalArgumentException("Input cannot be null");
- }
- 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<E> leftSet = new HashSet<>();
- for (int i = 0; i < leftLength; i++) {
- leftSet.add(left.at(i));
- }
- final Set<E> rightSet = new HashSet<>();
- for (int i = 0; i < rightLength; i++) {
- rightSet.add(right.at(i));
- }
- final Set<E> unionSet = new HashSet<>(leftSet);
- unionSet.addAll(rightSet);
- final int intersectionSize = leftSet.size() + rightSet.size() - unionSet.size();
- return 1.0d * intersectionSize / unionSet.size();
- }
- }