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.math.stat.descriptive.summary;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;
22
23 /**
24 * Returns the product of the available values.
25 * <p>
26 * If there are no values in the dataset, or any of the values are
27 * <code>NaN</code>, then <code>NaN</code> is returned.</p>
28 * <p>
29 * <strong>Note that this implementation is not synchronized.</strong> If
30 * multiple threads access an instance of this class concurrently, and at least
31 * one of the threads invokes the <code>increment()</code> or
32 * <code>clear()</code> method, it must be synchronized externally.</p>
33 *
34 * @version $Revision: 617953 $ $Date: 2008-02-02 22:54:00 -0700 (Sat, 02 Feb 2008) $
35 */
36 public class Product extends AbstractStorelessUnivariateStatistic implements Serializable {
37
38 /** Serializable version identifier */
39 private static final long serialVersionUID = 2824226005990582538L;
40
41 /**The number of values that have been added */
42 private long n;
43
44 /**
45 * The current Running Product.
46 */
47 private double value;
48
49 /**
50 * Create a Product instance
51 */
52 public Product() {
53 n = 0;
54 value = Double.NaN;
55 }
56
57 /**
58 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#increment(double)
59 */
60 public void increment(final double d) {
61 if (n == 0) {
62 value = d;
63 } else {
64 value *= d;
65 }
66 n++;
67 }
68
69 /**
70 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getResult()
71 */
72 public double getResult() {
73 return value;
74 }
75
76 /**
77 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getN()
78 */
79 public long getN() {
80 return n;
81 }
82
83 /**
84 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#clear()
85 */
86 public void clear() {
87 value = Double.NaN;
88 n = 0;
89 }
90
91 /**
92 * Returns the product of the entries in the specified portion of
93 * the input array, or <code>Double.NaN</code> if the designated subarray
94 * is empty.
95 * <p>
96 * Throws <code>IllegalArgumentException</code> if the array is null.</p>
97 *
98 * @param values the input array
99 * @param begin index of the first array element to include
100 * @param length the number of elements to include
101 * @return the product of the values or Double.NaN if length = 0
102 * @throws IllegalArgumentException if the array is null or the array index
103 * parameters are not valid
104 */
105 public double evaluate(final double[] values, final int begin, final int length) {
106 double product = Double.NaN;
107 if (test(values, begin, length)) {
108 product = 1.0;
109 for (int i = begin; i < begin + length; i++) {
110 product *= values[i];
111 }
112 }
113 return product;
114 }
115
116 }