kinow commented on a change in pull request #109: TEXT-155: Add a generic IntersectionSimilarity measure URL: https://github.com/apache/commons-text/pull/109#discussion_r263985577
########## File path: src/main/java/org/apache/commons/text/similarity/IntersectionSimilarity.java ########## @@ -0,0 +1,197 @@ +/* + * 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.Collection; +import java.util.HashMap; +import java.util.Map; +import java.util.Set; +import java.util.function.Function; +import java.util.stream.Stream; + +/** + * Measures the intersection of two sets created from a pair of character sequences. + * + * <p>It is assumed that the type {@code T} correctly conforms to the requirements for storage + * within a {@link Set} or {@link HashMap}. Ideally the type is immutable and implements + * {@link Object#equals(Object)} and {@link Object#hashCode()}.</p> + * + * @param <T> the type of the elements extracted from the character sequence + * @since 1.7 + * @see Set + * @see HashMap + */ +public class IntersectionSimilarity<T> implements SimilarityScore<IntersectionResult> { + /** The converter used to create the elements from the characters. */ + private final Function<CharSequence, Collection<T>> converter; + + // The following is adapted from commons-collections for a Bag. + // A Bag is a collection that can store the count of the number + // of copies of each element. + + /** + * Mutable counter class for storing the count of elements. + */ + private static class BagCount { + /** The count. This is initialised to 1 upon construction. */ + int count = 1; + } + + /** + * A minimal implementation of a Bag that can store elements and a count. + * + * <p>For the intended purpose the Bag does not have to be a {@link Collection}. It does not + * even have to know its own size. + */ + private class TinyBag { + /** The backing map. */ + private final Map<T, BagCount> map; + + /** + * Create a new tiny bag. + * + * @param initialCapacity the initial capacity + */ + TinyBag(int initialCapacity) { + map = new HashMap<>(initialCapacity); + } + + /** + * Adds a new element to the bag, incrementing its count in the underlying map. + * + * @param object the object to add + */ + void add(T object) { + final BagCount mut = map.get(object); + if (mut == null) { + map.put(object, new BagCount()); + } else { + mut.count++; + } + } + + /** + * Returns the number of occurrence of the given element in this bag by + * looking up its count in the underlying map. + * + * @param object the object to search for + * @return the number of occurrences of the object, zero if not found + */ + int getCount(final Object object) { + final BagCount count = map.get(object); + if (count != null) { + return count.count; + } + return 0; + } + + /** + * Returns a possibly parallel Stream of all the entries in the bag. + * + * @return the stream + */ + Stream<Map.Entry<T, BagCount>> parallelStream() { + return map.entrySet().parallelStream(); + } Review comment: Returning a `parallelStream` might be bad here I think. Instead we should either default to normal stream, or give the user a way to choose whether to use a normal or a parallel stream (example [discussion about it](https://stackoverflow.com/questions/48471554/java-parallel-stream-use-or-not-to-use) with some good references). I had an issue with a parallel stream in a library some months ago, and took a while to identify where the problem was (it involved returning gridded data from an ArcGIS server in a JAXB web service in a legacy app being ported to Java 8... not the best of the experiences troubleshooting that). ---------------------------------------------------------------- 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: [email protected] With regards, Apache Git Services
