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    }