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Apache Commons Text is a library focused on algorithms working on strings.
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/*
* 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.
*
*
* For further explanation about Jaccard Similarity, refer https://en.wikipedia.org/wiki/Jaccard_index
*
*
* @since 1.0
*/
public class JaccardSimilarity implements SimilarityScore {
/**
* Singleton instance.
*/
static final JaccardSimilarity INSTANCE = new JaccardSimilarity();
/**
* 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 The type of similarity score unit.
* @param left first input sequence.
* @param right second input sequence.
* @return index.
* @since 1.13.0
*/
public Double apply(final SimilarityInput left, final SimilarityInput 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 leftSet = new HashSet<>();
for (int i = 0; i < leftLength; i++) {
leftSet.add(left.at(i));
}
final Set rightSet = new HashSet<>();
for (int i = 0; i < rightLength; i++) {
rightSet.add(right.at(i));
}
final Set unionSet = new HashSet<>(leftSet);
unionSet.addAll(rightSet);
final int intersectionSize = leftSet.size() + rightSet.size() - unionSet.size();
return 1.0d * intersectionSize / unionSet.size();
}
}
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