stddev.hpp

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# /*
#  * Created by YongGyu Lee on 2020/12/08.
#  */
#
# ifndef VCCC_NUMERIC_STDDEV_HPP
# define VCCC_NUMERIC_STDDEV_HPP
#
# include <cmath>
#
# include "vccc/__numeric/average.hpp"
 
namespace vccc {
 
template<typename InputIterator, typename T,
         std::enable_if_t<is_iterator<InputIterator>::value, int> = 0>
inline auto
stddev(InputIterator first, InputIterator last, T avg)
{
  return std::sqrt(
      sum(first, last, [avg](const auto& next) { return square(next - avg); })
          / static_cast<decay_if_float_t<T>>(std::distance(first, last)) // TODO: subtract 1
  );
}
 
template<typename InputIterator, std::enable_if_t<is_iterable<InputIterator>::value, int> = 0>
inline auto
stddev(InputIterator first, InputIterator last)
{
  return stddev(first, last, average(first, last));
}
 
template<typename ...Numbers, std::enable_if_t<negation<disjunction<is_iterable<Numbers>...>>::value, int> = 0>
inline auto
stddev(Numbers... numbers)
{
  return std::sqrt(
      sum_custom([avg = average(numbers...)](auto next) { return square(next - avg); }, numbers...)
          / static_cast<decay_if_float_t < Numbers... >> (sizeof...(Numbers))
  );
}
 
 
template<typename InputIterator>
auto
avg_stddev(InputIterator first, InputIterator last)
{
  auto avg = average(first, last);
  return std::make_pair(avg, stddev(first, last, avg));
}
 
 
} // namespace vccc
 
# endif // VCCC_NUMERIC_STDDEV_HPP