org.simmetrics.metrics.GeneralizedOverlapCoefficient.java Source code

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Here is the source code for org.simmetrics.metrics.GeneralizedOverlapCoefficient.java

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/*
 * #%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";
    }

}