#ifndef STL_STATISTICS_H
#define STL_STATISTICS_H
// Computes average and standard deviation 
// for data stored in std::vector container
#include <vector>
#include <algorithm>
#include <numeric>
#include <cmath>

using namespace std;

// Average
double get_ave(const vector<double> & x)
{
  // average = sum_i=1^N x_i /N
  // sum up values, initial value 0
  double sum = accumulate(x.begin(),x.end(),0); 
  return (sum/x.size());
}


// Standard deviation; known average
double get_sigma(const vector<double>& x, double & ave)
{
  //              sum_i=1^N (x_i-<x>)^2  
  // sigma = sqrt( -------------------- )
  //                    N-1              
  // 
  // 
  //         (x-<x>).(x-<x>)
  // = sqrt( --------------- )
  //             N-1
  // subtract ave from all elements ; store to xx
  vector<double> xx(x);
  int N = x.size();  
  transform(x.begin(),x.end(),xx.begin(),bind2nd(minus<double>(),ave));
  double sigma = inner_product(xx.begin(),xx.end(),xx.begin(),0);
  sigma = sqrt(sigma/(N-1));
  return sigma;
}

#endif