    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.math3.stat.descriptive.summary;
    018
    019    import java.io.Serializable;
    020
    021    import org.apache.commons.math3.exception.MathIllegalArgumentException;
    022    import org.apache.commons.math3.exception.NullArgumentException;
    023    import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
    024    import org.apache.commons.math3.stat.descriptive.WeightedEvaluation;
    025    import org.apache.commons.math3.util.FastMath;
    026    import org.apache.commons.math3.util.MathUtils;
    027
    028    /**
    029     * Returns the product of the available values.
    030     * <p>
    031     * If there are no values in the dataset, then 1 is returned.
    032     *  If any of the values are
    033     * <code>NaN</code>, then <code>NaN</code> is returned.</p>
    034     * <p>
    035     * <strong>Note that this implementation is not synchronized.</strong> If
    036     * multiple threads access an instance of this class concurrently, and at least
    037     * one of the threads invokes the <code>increment()</code> or
    038     * <code>clear()</code> method, it must be synchronized externally.</p>
    039     *
    040     * @version $Id: Product.java 1416643 2012-12-03 19:37:14Z tn $
    041     */
    042    public class Product extends AbstractStorelessUnivariateStatistic implements Serializable, WeightedEvaluation {
    043
    044        /** Serializable version identifier */
    045        private static final long serialVersionUID = 2824226005990582538L;
    046
    047        /**The number of values that have been added */
    048        private long n;
    049
    050        /**
    051         * The current Running Product.
    052         */
    053        private double value;
    054
    055        /**
    056         * Create a Product instance
    057         */
    058        public Product() {
    059            n = 0;
    060            value = 1;
    061        }
    062
    063        /**
    064         * Copy constructor, creates a new {@code Product} identical
    065         * to the {@code original}
    066         *
    067         * @param original the {@code Product} instance to copy
    068         * @throws NullArgumentException  if original is null
    069         */
    070        public Product(Product original) throws NullArgumentException {
    071            copy(original, this);
    072        }
    073
    074        /**
    075         * {@inheritDoc}
    076         */
    077        @Override
    078        public void increment(final double d) {
    079            value *= d;
    080            n++;
    081        }
    082
    083        /**
    084         * {@inheritDoc}
    085         */
    086        @Override
    087        public double getResult() {
    088            return value;
    089        }
    090
    091        /**
    092         * {@inheritDoc}
    093         */
    094        public long getN() {
    095            return n;
    096        }
    097
    098        /**
    099         * {@inheritDoc}
    100         */
    101        @Override
    102        public void clear() {
    103            value = 1;
    104            n = 0;
    105        }
    106
    107        /**
    108         * Returns the product of the entries in the specified portion of
    109         * the input array, or <code>Double.NaN</code> if the designated subarray
    110         * is empty.
    111         * <p>
    112         * Throws <code>MathIllegalArgumentException</code> if the array is null.</p>
    113         *
    114         * @param values the input array
    115         * @param begin index of the first array element to include
    116         * @param length the number of elements to include
    117         * @return the product of the values or 1 if length = 0
    118         * @throws MathIllegalArgumentException if the array is null or the array index
    119         *  parameters are not valid
    120         */
    121        @Override
    122        public double evaluate(final double[] values, final int begin, final int length)
    123        throws MathIllegalArgumentException {
    124            double product = Double.NaN;
    125            if (test(values, begin, length, true)) {
    126                product = 1.0;
    127                for (int i = begin; i < begin + length; i++) {
    128                    product *= values[i];
    129                }
    130            }
    131            return product;
    132        }
    133
    134        /**
    135         * <p>Returns the weighted product of the entries in the specified portion of
    136         * the input array, or <code>Double.NaN</code> if the designated subarray
    137         * is empty.</p>
    138         *
    139         * <p>Throws <code>MathIllegalArgumentException</code> if any of the following are true:
    140         * <ul><li>the values array is null</li>
    141         *     <li>the weights array is null</li>
    142         *     <li>the weights array does not have the same length as the values array</li>
    143         *     <li>the weights array contains one or more infinite values</li>
    144         *     <li>the weights array contains one or more NaN values</li>
    145         *     <li>the weights array contains negative values</li>
    146         *     <li>the start and length arguments do not determine a valid array</li>
    147         * </ul></p>
    148         *
    149         * <p>Uses the formula, <pre>
    150         *    weighted product = &prod;values[i]<sup>weights[i]</sup>
    151         * </pre>
    152         * that is, the weights are applied as exponents when computing the weighted product.</p>
    153         *
    154         * @param values the input array
    155         * @param weights the weights array
    156         * @param begin index of the first array element to include
    157         * @param length the number of elements to include
    158         * @return the product of the values or 1 if length = 0
    159         * @throws MathIllegalArgumentException if the parameters are not valid
    160         * @since 2.1
    161         */
    162        public double evaluate(final double[] values, final double[] weights,
    163            final int begin, final int length) throws MathIllegalArgumentException {
    164            double product = Double.NaN;
    165            if (test(values, weights, begin, length, true)) {
    166                product = 1.0;
    167                for (int i = begin; i < begin + length; i++) {
    168                    product *= FastMath.pow(values[i], weights[i]);
    169                }
    170            }
    171            return product;
    172        }
    173
    174        /**
    175         * <p>Returns the weighted product of the entries in the input array.</p>
    176         *
    177         * <p>Throws <code>MathIllegalArgumentException</code> if any of the following are true:
    178         * <ul><li>the values array is null</li>
    179         *     <li>the weights array is null</li>
    180         *     <li>the weights array does not have the same length as the values array</li>
    181         *     <li>the weights array contains one or more infinite values</li>
    182         *     <li>the weights array contains one or more NaN values</li>
    183         *     <li>the weights array contains negative values</li>
    184         * </ul></p>
    185         *
    186         * <p>Uses the formula, <pre>
    187         *    weighted product = &prod;values[i]<sup>weights[i]</sup>
    188         * </pre>
    189         * that is, the weights are applied as exponents when computing the weighted product.</p>
    190         *
    191         * @param values the input array
    192         * @param weights the weights array
    193         * @return the product of the values or Double.NaN if length = 0
    194         * @throws MathIllegalArgumentException if the parameters are not valid
    195         * @since 2.1
    196         */
    197        public double evaluate(final double[] values, final double[] weights)
    198        throws MathIllegalArgumentException {
    199            return evaluate(values, weights, 0, values.length);
    200        }
    201
    202
    203        /**
    204         * {@inheritDoc}
    205         */
    206        @Override
    207        public Product copy() {
    208            Product result = new Product();
    209            // No try-catch or advertised exception because args are valid
    210            copy(this, result);
    211            return result;
    212        }
    213
    214        /**
    215         * Copies source to dest.
    216         * <p>Neither source nor dest can be null.</p>
    217         *
    218         * @param source Product to copy
    219         * @param dest Product to copy to
    220         * @throws NullArgumentException if either source or dest is null
    221         */
    222        public static void copy(Product source, Product dest)
    223            throws NullArgumentException {
    224            MathUtils.checkNotNull(source);
    225            MathUtils.checkNotNull(dest);
    226            dest.setData(source.getDataRef());
    227            dest.n = source.n;
    228            dest.value = source.value;
    229        }
    230
    231    }