1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.statistics.descriptive;
18
19 /**
20 * Returns the product of the available values.
21 *
22 * <ul>
23 * <li>The result is one if no values are observed.
24 * <li>The result is {@code NaN} if any of the values is {@code NaN}.
25 * </ul>
26 *
27 * <p>This class is designed to work with (though does not require)
28 * {@linkplain java.util.stream streams}.
29 *
30 * <p><strong>This instance is not thread safe.</strong>
31 * If multiple threads access an instance of this class concurrently,
32 * and at least one of the threads invokes the {@link java.util.function.DoubleConsumer#accept(double) accept} or
33 * {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
34 *
35 * <p>However, it is safe to use {@link java.util.function.DoubleConsumer#accept(double) accept}
36 * and {@link StatisticAccumulator#combine(StatisticResult) combine}
37 * as {@code accumulator} and {@code combiner} functions of
38 * {@link java.util.stream.Collector Collector} on a parallel stream,
39 * because the parallel instance of {@link java.util.stream.Stream#collect Stream.collect()}
40 * provides the necessary partitioning, isolation, and merging of results for
41 * safe and efficient parallel execution.
42 *
43 * @since 1.1
44 */
45 public final class Product implements DoubleStatistic, StatisticAccumulator<Product> {
46
47 /** Product of all values. */
48 private double productValue = 1;
49
50 /**
51 * Create an instance.
52 */
53 private Product() {
54 // No-op
55 }
56
57 /**
58 * Creates an instance.
59 *
60 * <p>The initial result is one.
61 *
62 * @return {@code Product} instance.
63 */
64 public static Product create() {
65 return new Product();
66 }
67
68 /**
69 * Returns an instance populated using the input {@code values}.
70 *
71 * <p>The result is {@code NaN} if any of the values is {@code NaN}
72 * or the product at any point is a {@code NaN}.
73 *
74 * <p>When the input is an empty array, the result is one.
75 *
76 * @param values Values.
77 * @return {@code Product} instance.
78 */
79 public static Product of(double... values) {
80 return Statistics.add(new Product(), values);
81 }
82
83 /**
84 * Returns an instance populated using the specified range of {@code values}.
85 *
86 * <p>The result is {@code NaN} if any of the values is {@code NaN}
87 * or the product at any point is a {@code NaN}.
88 *
89 * <p>When the range is empty, the result is one.
90 *
91 * @param values Values.
92 * @param from Inclusive start of the range.
93 * @param to Exclusive end of the range.
94 * @return {@code Product} instance.
95 * @throws IndexOutOfBoundsException if the sub-range is out of bounds
96 * @since 1.2
97 */
98 public static Product ofRange(double[] values, int from, int to) {
99 Statistics.checkFromToIndex(from, to, values.length);
100 return createFromRange(values, from, to);
101 }
102
103 /**
104 * Create an instance using the specified range of {@code values}.
105 *
106 * <p>Warning: No range checks are performed.
107 *
108 * @param values Values.
109 * @param from Inclusive start of the range.
110 * @param to Exclusive end of the range.
111 * @return {@code Product} instance.
112 */
113 static Product createFromRange(double[] values, int from, int to) {
114 return Statistics.add(new Product(), values, from, to);
115 }
116
117 /**
118 * Returns an instance populated using the input {@code values}.
119 *
120 * <p>When the input is an empty array, the result is one.
121 *
122 * @param values Values.
123 * @return {@code Product} instance.
124 */
125 public static Product of(int... values) {
126 return Statistics.add(new Product(), values);
127 }
128
129 /**
130 * Returns an instance populated using the specified range of {@code values}.
131 *
132 * <p>When the range is empty, the result is one.
133 *
134 * @param values Values.
135 * @param from Inclusive start of the range.
136 * @param to Exclusive end of the range.
137 * @return {@code Product} instance.
138 * @throws IndexOutOfBoundsException if the sub-range is out of bounds
139 * @since 1.2
140 */
141 public static Product ofRange(int[] values, int from, int to) {
142 Statistics.checkFromToIndex(from, to, values.length);
143 return createFromRange(values, from, to);
144 }
145
146 /**
147 * Create an instance using the specified range of {@code values}.
148 *
149 * <p>Warning: No range checks are performed.
150 *
151 * @param values Values.
152 * @param from Inclusive start of the range.
153 * @param to Exclusive end of the range.
154 * @return {@code Product} instance.
155 */
156 static Product createFromRange(int[] values, int from, int to) {
157 return Statistics.add(new Product(), values, from, to);
158 }
159
160 /**
161 * Returns an instance populated using the input {@code values}.
162 *
163 * <p>When the input is an empty array, the result is one.
164 *
165 * @param values Values.
166 * @return {@code Product} instance.
167 */
168 public static Product of(long... values) {
169 return Statistics.add(new Product(), values);
170 }
171
172 /**
173 * Returns an instance populated using the specified range of {@code values}.
174 *
175 * <p>When the range is empty, the result is one.
176 *
177 * @param values Values.
178 * @param from Inclusive start of the range.
179 * @param to Exclusive end of the range.
180 * @return {@code Product} instance.
181 * @throws IndexOutOfBoundsException if the sub-range is out of bounds
182 * @since 1.2
183 */
184 public static Product ofRange(long[] values, int from, int to) {
185 Statistics.checkFromToIndex(from, to, values.length);
186 return createFromRange(values, from, to);
187 }
188
189 /**
190 * Create an instance using the specified range of {@code values}.
191 *
192 * <p>Warning: No range checks are performed.
193 *
194 * @param values Values.
195 * @param from Inclusive start of the range.
196 * @param to Exclusive end of the range.
197 * @return {@code Product} instance.
198 */
199 static Product createFromRange(long[] values, int from, int to) {
200 return Statistics.add(new Product(), values, from, to);
201 }
202
203 /**
204 * Updates the state of the statistic to reflect the addition of {@code value}.
205 *
206 * @param value Value.
207 */
208 @Override
209 public void accept(double value) {
210 this.productValue *= value;
211 }
212
213 /**
214 * Gets the product of all input values.
215 *
216 * <p>When no values have been added, the result is one.
217 *
218 * @return product of all values.
219 */
220 @Override
221 public double getAsDouble() {
222 return productValue;
223 }
224
225 @Override
226 public Product combine(Product other) {
227 productValue *= other.productValue;
228 return this;
229 }
230 }