org.apache.commons.math3.ml.clustering.evaluation.ClusterEvaluator Maven / Gradle / Ivy
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* 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.math3.ml.clustering.evaluation;
import java.util.List;
import org.apache.commons.math3.ml.clustering.CentroidCluster;
import org.apache.commons.math3.ml.clustering.Cluster;
import org.apache.commons.math3.ml.clustering.Clusterable;
import org.apache.commons.math3.ml.clustering.DoublePoint;
import org.apache.commons.math3.ml.distance.DistanceMeasure;
import org.apache.commons.math3.ml.distance.EuclideanDistance;
/**
* Base class for cluster evaluation methods.
*
* @param type of the clustered points
* @since 3.3
*/
public abstract class ClusterEvaluator {
/** The distance measure to use when evaluating the cluster. */
private final DistanceMeasure measure;
/**
* Creates a new cluster evaluator with an {@link EuclideanDistance}
* as distance measure.
*/
public ClusterEvaluator() {
this(new EuclideanDistance());
}
/**
* Creates a new cluster evaluator with the given distance measure.
* @param measure the distance measure to use
*/
public ClusterEvaluator(final DistanceMeasure measure) {
this.measure = measure;
}
/**
* Computes the evaluation score for the given list of clusters.
* @param clusters the clusters to evaluate
* @return the computed score
*/
public abstract double score(List> clusters);
/**
* Returns whether the first evaluation score is considered to be better
* than the second one by this evaluator.
*
* Specific implementations shall override this method if the returned scores
* do not follow the same ordering, i.e. smaller score is better.
*
* @param score1 the first score
* @param score2 the second score
* @return {@code true} if the first score is considered to be better, {@code false} otherwise
*/
public boolean isBetterScore(double score1, double score2) {
return score1 < score2;
}
/**
* Calculates the distance between two {@link Clusterable} instances
* with the configured {@link DistanceMeasure}.
*
* @param p1 the first clusterable
* @param p2 the second clusterable
* @return the distance between the two clusterables
*/
protected double distance(final Clusterable p1, final Clusterable p2) {
return measure.compute(p1.getPoint(), p2.getPoint());
}
/**
* Computes the centroid for a cluster.
*
* @param cluster the cluster
* @return the computed centroid for the cluster,
* or {@code null} if the cluster does not contain any points
*/
protected Clusterable centroidOf(final Cluster cluster) {
final List points = cluster.getPoints();
if (points.isEmpty()) {
return null;
}
// in case the cluster is of type CentroidCluster, no need to compute the centroid
if (cluster instanceof CentroidCluster) {
return ((CentroidCluster) cluster).getCenter();
}
final int dimension = points.get(0).getPoint().length;
final double[] centroid = new double[dimension];
for (final T p : points) {
final double[] point = p.getPoint();
for (int i = 0; i < centroid.length; i++) {
centroid[i] += point[i];
}
}
for (int i = 0; i < centroid.length; i++) {
centroid[i] /= points.size();
}
return new DoublePoint(centroid);
}
}