code: /*
   * #%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.intersection;
  import static java.lang.Math.min;
  
  import org.simmetrics.MultisetMetric;
  import com.google.common.collect.Multiset;
  
  /**
   * The generalized overlap coefficient measures the overlap between two
   * multisets. The similarity is defined as the size of the intersection divided
   * by the smaller of the size of the two sets
   * <p>
   * <code>
   * similarity(q,r) = ∣q ∩ r∣ / min{∣q∣, ∣r∣}
   * </code>
   * <p>
   * Unlike the overlap coefficient the occurrence (cardinality) of an entry is
   * taken into account. E.g. {@code [hello, world]} and
   * {@code [hello, world, hello, world]} would be identical when compared with
   * the overlap coefficient index but are dissimilar when the generalized version
   * is used.
   * <p>
   * This class is immutable and thread-safe.
   * 
   * @param <T>
   *            type of the token
   * 
   * @see OverlapCoefficient
   * @see <a href="http://en.wikipedia.org/wiki/Overlap_coefficient">Wikipedia -
   *      Overlap Coefficient</a>
   */
  public final class GeneralizedOverlapCoefficient<T> implements
  		MultisetMetric<T> {
  
  	@Override
  	public float compare(Multiset<T> a, Multiset<T> b) {
  
  		if (a.isEmpty() && b.isEmpty()) {
  			return 1.0f;
  		}
  
  		if (a.isEmpty() || b.isEmpty()) {
  			return 0.0f;
  		}
  
  		// ∣q ∩ r∣ / min{∣q∣, ∣r∣}
  		return intersection(a, b).size() / (float) min(a.size(), b.size());
  	}
  
  	@Override
  	public String toString() {
  		return "GeneralizedOverlapCoefficient";
  	}
  
  }
  