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Diffstat (limited to 'include/gudhi/pick_n_random_points.h')
-rw-r--r-- | include/gudhi/pick_n_random_points.h | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/include/gudhi/pick_n_random_points.h b/include/gudhi/pick_n_random_points.h new file mode 100644 index 00000000..f0e3f1f1 --- /dev/null +++ b/include/gudhi/pick_n_random_points.h @@ -0,0 +1,86 @@ +/* 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_SUBS_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_SUBS_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_ |