001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.math4.legacy.ml.clustering;
019
020import java.util.ArrayList;
021import java.util.List;
022
023/**
024 * Cluster holding a set of {@link Clusterable} points.
025 * @param <T> the type of points that can be clustered
026 * @since 3.2
027 */
028public class Cluster<T extends Clusterable> {
029
030    /** The points contained in this cluster. */
031    private final List<T> points;
032
033    /**
034     * Build a cluster centered at a specified point.
035     */
036    public Cluster() {
037        points = new ArrayList<>();
038    }
039
040    /**
041     * Add a point to this cluster.
042     * @param point point to add
043     */
044    public void addPoint(final T point) {
045        points.add(point);
046    }
047
048    /**
049     * Get the points contained in the cluster.
050     * @return points contained in the cluster
051     */
052    public List<T> getPoints() {
053        return points;
054    }
055
056    /**
057     * Computes the centroid of the cluster.
058     *
059     * @return the centroid for the cluster, or {@code null} if the
060     * cluster does not contain any points.
061     */
062    public Clusterable centroid() {
063        if (points.isEmpty()) {
064            return null;
065        } else {
066            final int dimension = points.get(0).getPoint().length;
067            final double[] centroid = new double[dimension];
068            for (final T p : points) {
069                final double[] point = p.getPoint();
070                for (int i = 0; i < centroid.length; i++) {
071                    centroid[i] += point[i];
072                }
073            }
074            for (int i = 0; i < centroid.length; i++) {
075                centroid[i] /= points.size();
076            }
077            return new DoublePoint(centroid);
078        }
079    }
080}