bbeta.hpp

// Copyright © 2020 Thomas Nagler
//
// This file is part of the wdm library and licensed under the terms of
// the MIT license. For a copy, see the LICENSE file in the root directory
// or https://github.com/tnagler/wdm/blob/master/LICENSE.
 
#pragma once
 
#include "ranks.hpp"
#include "utils.hpp"
 
namespace wdm {
 
namespace impl {
 
inline double
bbeta(const std::vector<double>& x,
      const std::vector<double>& y,
      std::vector<double> weights = std::vector<double>())
{
  utils::check_sizes(x, y, weights);
  size_t n = x.size();
 
  // find the medians
  double med_x = impl::median(x, weights);
  double med_y = impl::median(y, weights);
 
  if (weights.size() == 0)
    weights = std::vector<double>(n, 1.0);
 
  // count elements in lower left and upper right quadrants
  double w_acc{ 0.0 };
  for (size_t i = 0; i < n; i++) {
    if ((x[i] <= med_x) && (y[i] <= med_y))
      w_acc += weights[i];
    else if ((x[i] > med_x) && (y[i] > med_y))
      w_acc += weights[i];
  }
 
  return 2 * w_acc / utils::sum(weights) - 1;
}
 
}
 
}