    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    package org.apache.commons.math.stat.descriptive.summary;
    018
    019    import java.io.Serializable;
    020
    021    import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;
    022    import org.apache.commons.math.stat.descriptive.WeightedEvaluation;
    023    import org.apache.commons.math.util.FastMath;
    024
    025    /**
    026     * Returns the product of the available values.
    027     * <p>
    028     * If there are no values in the dataset, or any of the values are
    029     * <code>NaN</code>, then <code>NaN</code> is returned.</p>
    030     * <p>
    031     * <strong>Note that this implementation is not synchronized.</strong> If
    032     * multiple threads access an instance of this class concurrently, and at least
    033     * one of the threads invokes the <code>increment()</code> or
    034     * <code>clear()</code> method, it must be synchronized externally.</p>
    035     *
    036     * @version $Revision: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $
    037     */
    038    public class Product extends AbstractStorelessUnivariateStatistic implements Serializable, WeightedEvaluation {
    039
    040        /** Serializable version identifier */
    041        private static final long serialVersionUID = 2824226005990582538L;
    042
    043        /**The number of values that have been added */
    044        private long n;
    045
    046        /**
    047         * The current Running Product.
    048         */
    049        private double value;
    050
    051        /**
    052         * Create a Product instance
    053         */
    054        public Product() {
    055            n = 0;
    056            value = Double.NaN;
    057        }
    058
    059        /**
    060         * Copy constructor, creates a new {@code Product} identical
    061         * to the {@code original}
    062         *
    063         * @param original the {@code Product} instance to copy
    064         */
    065        public Product(Product original) {
    066            copy(original, this);
    067        }
    068
    069        /**
    070         * {@inheritDoc}
    071         */
    072        @Override
    073        public void increment(final double d) {
    074            if (n == 0) {
    075                value = d;
    076            } else {
    077                value *= d;
    078            }
    079            n++;
    080        }
    081
    082        /**
    083         * {@inheritDoc}
    084         */
    085        @Override
    086        public double getResult() {
    087            return value;
    088        }
    089
    090        /**
    091         * {@inheritDoc}
    092         */
    093        public long getN() {
    094            return n;
    095        }
    096
    097        /**
    098         * {@inheritDoc}
    099         */
    100        @Override
    101        public void clear() {
    102            value = Double.NaN;
    103            n = 0;
    104        }
    105
    106        /**
    107         * Returns the product of the entries in the specified portion of
    108         * the input array, or <code>Double.NaN</code> if the designated subarray
    109         * is empty.
    110         * <p>
    111         * Throws <code>IllegalArgumentException</code> if the array is null.</p>
    112         *
    113         * @param values the input array
    114         * @param begin index of the first array element to include
    115         * @param length the number of elements to include
    116         * @return the product of the values or Double.NaN if length = 0
    117         * @throws IllegalArgumentException if the array is null or the array index
    118         *  parameters are not valid
    119         */
    120        @Override
    121        public double evaluate(final double[] values, final int begin, final int length) {
    122            double product = Double.NaN;
    123            if (test(values, begin, length)) {
    124                product = 1.0;
    125                for (int i = begin; i < begin + length; i++) {
    126                    product *= values[i];
    127                }
    128            }
    129            return product;
    130        }
    131
    132        /**
    133         * <p>Returns the weighted product of the entries in the specified portion of
    134         * the input array, or <code>Double.NaN</code> if the designated subarray
    135         * is empty.</p>
    136         *
    137         * <p>Throws <code>IllegalArgumentException</code> if any of the following are true:
    138         * <ul><li>the values array is null</li>
    139         *     <li>the weights array is null</li>
    140         *     <li>the weights array does not have the same length as the values array</li>
    141         *     <li>the weights array contains one or more infinite values</li>
    142         *     <li>the weights array contains one or more NaN values</li>
    143         *     <li>the weights array contains negative values</li>
    144         *     <li>the start and length arguments do not determine a valid array</li>
    145         * </ul></p>
    146         *
    147         * <p>Uses the formula, <pre>
    148         *    weighted product = &prod;values[i]<sup>weights[i]</sup>
    149         * </pre>
    150         * that is, the weights are applied as exponents when computing the weighted product.</p>
    151         *
    152         * @param values the input array
    153         * @param weights the weights array
    154         * @param begin index of the first array element to include
    155         * @param length the number of elements to include
    156         * @return the product of the values or Double.NaN if length = 0
    157         * @throws IllegalArgumentException if the parameters are not valid
    158         * @since 2.1
    159         */
    160        public double evaluate(final double[] values, final double[] weights,
    161                               final int begin, final int length) {
    162            double product = Double.NaN;
    163            if (test(values, weights, begin, length)) {
    164                product = 1.0;
    165                for (int i = begin; i < begin + length; i++) {
    166                    product *= FastMath.pow(values[i], weights[i]);
    167                }
    168            }
    169            return product;
    170        }
    171
    172        /**
    173         * <p>Returns the weighted product of the entries in the input array.</p>
    174         *
    175         * <p>Throws <code>IllegalArgumentException</code> if any of the following are true:
    176         * <ul><li>the values array is null</li>
    177         *     <li>the weights array is null</li>
    178         *     <li>the weights array does not have the same length as the values array</li>
    179         *     <li>the weights array contains one or more infinite values</li>
    180         *     <li>the weights array contains one or more NaN values</li>
    181         *     <li>the weights array contains negative values</li>
    182         * </ul></p>
    183         *
    184         * <p>Uses the formula, <pre>
    185         *    weighted product = &prod;values[i]<sup>weights[i]</sup>
    186         * </pre>
    187         * that is, the weights are applied as exponents when computing the weighted product.</p>
    188         *
    189         * @param values the input array
    190         * @param weights the weights array
    191         * @return the product of the values or Double.NaN if length = 0
    192         * @throws IllegalArgumentException if the parameters are not valid
    193         * @since 2.1
    194         */
    195        public double evaluate(final double[] values, final double[] weights) {
    196            return evaluate(values, weights, 0, values.length);
    197        }
    198
    199
    200        /**
    201         * {@inheritDoc}
    202         */
    203        @Override
    204        public Product copy() {
    205            Product result = new Product();
    206            copy(this, result);
    207            return result;
    208        }
    209
    210        /**
    211         * Copies source to dest.
    212         * <p>Neither source nor dest can be null.</p>
    213         *
    214         * @param source Product to copy
    215         * @param dest Product to copy to
    216         * @throws NullPointerException if either source or dest is null
    217         */
    218        public static void copy(Product source, Product dest) {
    219            dest.setData(source.getDataRef());
    220            dest.n = source.n;
    221            dest.value = source.value;
    222        }
    223
    224    }