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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 sum 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 Sum extends AbstractStorelessUnivariateStatistic implements Serializable {
37  
38      /** Serializable version identifier */
39      private static final long serialVersionUID = -8231831954703408316L;  
40        
41      /** */
42      private long n;
43      
44      /**
45       * The currently running sum.
46       */
47      private double value;
48  
49      /**
50       * Create a Sum instance
51       */
52      public Sum() {
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       * The sum 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 sum 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 sum = Double.NaN;
107         if (test(values, begin, length)) {
108             sum = 0.0;
109             for (int i = begin; i < begin + length; i++) {
110                 sum += values[i];
111             }
112         }
113         return sum;
114     }
115 
116 }