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/* This file is part of the Gudhi Library. The Gudhi library
* (Geometric Understanding in Higher Dimensions) is a generic C++
* library for computational topology.
*
* Author(s): Siargey Kachanovich
*
* Copyright (C) 2016 Inria
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef PICK_N_RANDOM_POINTS_H_
#define PICK_N_RANDOM_POINTS_H_
#include <gudhi/Clock.h>
#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 {
/**
* \ingroup subsampling
* \brief Subsample a point set by picking random vertices.
*
* \details It chooses `final_size` distinct points from a random access range `points`
* and outputs them to the output iterator `output_it`.
* Point_container::iterator should be ValueSwappable and RandomAccessIterator.
*/
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::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::random_device rd;
std::mt19937 g(rd());
std::shuffle(landmarks.begin(), landmarks.end(), g);
landmarks.resize(final_size);
for (int l : landmarks)
*output_it++ = points[l];
#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_
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