Math code snippet to get the mean and standard deviation of a std::vector.


#include <cassert>

#include <cmath>

#include <vector>



//From http://www.richelbilderbeek.nl/CppMeanAndStdDev.htm

void MeanAndStdDev(

  const std::vector<double>& myVector, 

  double& mean, 

  double& stdDev)

{

  const int size = static_cast<int>(myVector.size());

  assert(size>1);

  const double dSize = static_cast<double>(size);

  mean = 0.0;

  double sumX = 0.0;

  double sumXsquared = 0.0;

  for (int i=0; i!=size; ++i)

  {

    const double value = myVector[i];

    sumX+=value;

    sumXsquared+=(value*value);

    mean+=value;

  }



  mean/=dSize;

  stdDev = std::sqrt(((dSize*sumXsquared)-(sumX*sumX))/(dSize *(dSize-1.0)));

}

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(C++) MeanAndStdDev