1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef _CENTRAL_TENDENCY_STATISTICS_H
18#define _CENTRAL_TENDENCY_STATISTICS_H
19
20#include <math.h>
21
22// Not multithread safe
23class CentralTendencyStatistics {
24
25public:
26
27    CentralTendencyStatistics() :
28            mMean(NAN), mMedian(NAN), mMinimum(INFINITY), mMaximum(-INFINITY), mN(0), mM2(0),
29            mVariance(NAN), mVarianceKnownForN(0), mStddev(NAN), mStddevKnownForN(0) { }
30
31    ~CentralTendencyStatistics() { }
32
33    // add x to the set of samples
34    void sample(double x);
35
36    // return the arithmetic mean of all samples so far
37    double mean() const { return mMean; }
38
39    // return the minimum of all samples so far
40    double minimum() const { return mMinimum; }
41
42    // return the maximum of all samples so far
43    double maximum() const { return mMaximum; }
44
45    // return the variance of all samples so far
46    double variance() const;
47
48    // return the standard deviation of all samples so far
49    double stddev() const;
50
51    // return the number of samples added so far
52    unsigned n() const { return mN; }
53
54    // reset the set of samples to be empty
55    void reset();
56
57private:
58    double mMean;
59    double mMedian;
60    double mMinimum;
61    double mMaximum;
62    unsigned mN;    // number of samples so far
63    double mM2;
64
65    // cached variance, and n at time of caching
66    mutable double mVariance;
67    mutable unsigned mVarianceKnownForN;
68
69    // cached standard deviation, and n at time of caching
70    mutable double mStddev;
71    mutable unsigned mStddevKnownForN;
72
73};
74
75#endif // _CENTRAL_TENDENCY_STATISTICS_H
76