Java tutorial
/* * #%L * Simmetrics Core * %% * Copyright (C) 2014 - 2016 Simmetrics Authors * %% * Licensed 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. * #L% */ package org.simmetrics.metrics; import static org.simmetrics.metrics.Math.union; import static java.lang.Math.sqrt; import org.simmetrics.MultisetDistance; import org.simmetrics.MultisetMetric; import com.google.common.collect.Multiset; /** * Calculates the Euclidean distance and similarity over two multisets. * <p> * <code> * similarity(a,b) = 1 - distance(a,b) / (a + b) * <br> * distance(a,b) = a - b * </code> * <p> * This class is immutable and thread-safe. * * @see <a href="https://en.wikipedia.org/wiki/Euclidean_distance">Wikipedia - Euclidean Distance</a> * @param <T> * type of the token * */ public final class EuclideanDistance<T> implements MultisetMetric<T>, MultisetDistance<T> { @Override public float compare(Multiset<T> a, Multiset<T> b) { if (a.isEmpty() && b.isEmpty()) { return 1.0f; } float maxDistance = (float) sqrt((a.size() * a.size()) + (b.size() * b.size())); return 1.0f - distance(a, b) / maxDistance; } @Override public float distance(Multiset<T> a, Multiset<T> b) { float distance = 0.0f; for (T token : union(a, b).elementSet()) { float frequencyInA = a.count(token); float frequencyInB = b.count(token); distance += ((frequencyInA - frequencyInB) * (frequencyInA - frequencyInB)); } return (float) sqrt(distance); } @Override public String toString() { return "EuclideanDistance"; } }