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 = ∏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 = ∏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 }