aherbert commented on a change in pull request #103: TEXT-126: Adding Sorensen-Dice similarity algoritham URL: https://github.com/apache/commons-text/pull/103#discussion_r261841223
########## File path: src/main/java/org/apache/commons/text/similarity/SorensenDicesSimilarity.java ########## @@ -0,0 +1,74 @@ +/* + * 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; + +/** + * + * @since 1.7 + */ +public class SorensenDicesSimilarity implements SimilarityScore<Double> { + + /** + * @param left the first CharSequence, must not be null + * @param right the second CharSequence, must not be null + * @return result similarity + * @throws IllegalArgumentException if either CharSequence input is {@code null} + */ + + @Override + public Double apply(final CharSequence left, final CharSequence right) { + + if (left == null || right == null) { + throw new IllegalArgumentException("CharSequences must not be null"); + } + + if (left.equals(right)) { + return 1d; + } + + if ("".equals(left) || "".equals(right)) { Review comment: The line above the length comparison has an attempt at testing for equality: ``` if (left.equals(right)) { return 1d; } ``` So the code will not reach the length check anyway. However I note that the use of `equals` is actually invalid. It is not defined in the `CharSequence` interface and so comparing a `String` with a `StringBuilder` would fail even if they have the same chars because `String.equals` only matches other `String` objects. Note also that this is an algorithm that does comparisons using at least two characters. So inputting a single character is not valid for the main algorithm processing. It needs to be handled as an edge case. So handling char sequences of a single character should return 1 or 0 (because there are no bigrams). It makes more sense to return 1. The decision needs to be in the Javadoc. I would vote for returning 1. Here are the edge cases and proposed results: ``` null vs null IllegalArgumentException "" vs "" 1 "a" vs "a" 1 "ab" vs "ab" 1 "abc" vs "abd" 0.5 { [ab][bc] verses [ab][bd] = 2 * 1 / (2 + 2) } ``` So you need something like: ``` if (left == null || right == null) { throw new IllegalArgumentException("CharSequences must not be null"); } // Edge case for equality. Use Commons-Lang StringUtils which is a project dependency. if (StringUtils.equals(left, right)) { return 1d; } // Edge case for input not analysed by the algorithm if (left.length() <= 2 || right.length() <= 2) { // No bigrams return 0d; } ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
