org.simmetrics.metrics.GeneralizedOverlapCoefficient Maven / Gradle / Ivy
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* Simmetrics Core
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* Copyright (C) 2014 - 2015 Simmetrics Authors
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* http://www.apache.org/licenses/LICENSE-2.0
*
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package org.simmetrics.metrics;
import static com.google.common.collect.Multisets.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
*
*
* similarity(q,r) = ∣q ∩ r∣ / min{∣q∣, ∣r∣}
*
*
* 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.
*
* This class is immutable and thread-safe.
*
* @param
* type of the token
*
* @see OverlapCoefficient
* @see Wikipedia -
* Overlap Coefficient
*/
public final class GeneralizedOverlapCoefficient implements
MultisetMetric {
@Override
public float compare(Multiset a, Multiset b) {
if (a.isEmpty() && b.isEmpty()) {
return 1.0f;
}
if (a.isEmpty() || b.isEmpty()) {
return 0.0f;
}
// Smaller set first for performance improvement.
// See: MultisetIntersectionSize benchmark
if(a.size() > b.size()){
final Multiset swap = a; a = b; b = swap;
}
// ∣q ∩ r∣ / min{∣q∣, ∣r∣}
return intersection(a, b).size() / (float) min(a.size(), b.size());
}
@Override
public String toString() {
return "GeneralizedOverlapCoefficient";
}
}