Wednesday 4 January 2017

Statistics in C++ (Mean, Median and Standard Deviation)

Just a few simple statistics. I found this function extremely useful for my software DASOS. I used it for calculating features that may characterise trees. :)

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <numeric>
#include <cmath>

typedef struct Statistics {
   double mean;
   double median;
   double stdev;
} Statistics;

Statistics getMeanMedianStd(
        const std::vector<  double > &i_vector
        )
{
   Statistics stats;
   std::vector <  double  > vector(i_vector);
   std::sort(vector.begin(),vector.end());
   double sumD = std::accumulate(vector.begin(),vector.end(),0.0);
   stats.mean = sumD/double(vector.size());
   std::vector < double  > Diff(vector.size());
   std::transform(vector.begin(),vector.end(),Diff.begin(),
                  std::bind2nd(std::minus< double  > (),stats.mean));
   stats.stdev  = std::inner_product(Diff.begin(),Diff.end(),
                                      Diff.begin(),0.0);
   stats.median = vector[std::floor(double(vector.size())/2.0)];
   stats.stdev = std::sqrt(stats.stdev/vector.size());
   return stats;
}

int main(int argc, char *argv[])
{
    std::vector < double  > values({10.0,12.0,11.0,4.5,10,13,22,2,1});
       for(unsigned int i=0; i < values.size(); ++i)
       {
          std::cout << values[i] << " " ;
       }
       std::cout << "\n";
       Statistics stats = getMeanMedianStd(values);
       std::cout << "Mean               = " << stats.mean   << "\n"
                 << "Median             = " << stats.median << "\n"
                 << "Standard Deviation = " << stats.stdev  << "\n";
    std::cout << "   ***   EXIT   ***\n";
    return EXIT_SUCCESS;
}

PS: for the median if the array contains an even number of values, then the bigger one is chosen between the two of them.