pick_n_random_points.h

/*    This file is part of the Gudhi Library - https://gudhi.inria.fr/ - which is released under MIT.
 *    See file LICENSE or go to https://gudhi.inria.fr/licensing/ for full license details.
 *    Author(s):       Siargey Kachanovich
 *
 *    Copyright (C) 2016 Inria
 *
 *    Modification(s):
 *      - YYYY/MM Author: Description of the modification
 */
 
#ifndef PICK_N_RANDOM_POINTS_H_
#define PICK_N_RANDOM_POINTS_H_
 
#ifdef GUDHI_SUBSAMPLING_PROFILING
# include <gudhi/Clock.h>
#endif
 
#include <boost/range/size.hpp>
 
#include <cstddef>
#include <random>     // random_device, mt19937
#include <algorithm>  // shuffle
#include <numeric>    // iota
#include <iterator>
#include <vector>
 
 
namespace Gudhi {
 
namespace subsampling {
 
template <typename Point_container,
typename OutputIterator>
void pick_n_random_points(Point_container const &points,
                          std::size_t final_size,
                          OutputIterator output_it) {
#ifdef GUDHI_SUBSAMPLING_PROFILING
  Gudhi::Clock t;
#endif
 
  std::random_device rd;
  std::mt19937 g(rd());
 
#if __cplusplus >= 201703L
  std::sample(std::begin(points), std::end(points), output_it, final_size, g);
#else
  std::size_t nbP = boost::size(points);
  if (final_size > nbP)
      final_size = nbP;
 
  std::vector<int> landmarks(nbP);
  std::iota(landmarks.begin(), landmarks.end(), 0);
 
  std::shuffle(landmarks.begin(), landmarks.end(), g);
  landmarks.resize(final_size);
 
  for (int l : landmarks)
    *output_it++ = points[l];
#endif
 
#ifdef GUDHI_SUBSAMPLING_PROFILING
  t.end();
  std::cerr << "Random landmark choice took " << t.num_seconds()
      << " seconds." << std::endl;
#endif
}
 
}  // namespace subsampling
 
}  // namespace Gudhi
 
#endif  // PICK_N_RANDOM_POINTS_H_