Renamed pick_random_points -> pick_n_random_points

git-svn-id: svn+ssh://scm.gforge.inria.fr/svnroot/gudhi/branches/subsampling_and_spatialsearching@1516 636b058d-ea47-450e-bf9e-a15bfbe3eedb

Former-commit-id: 45cc8cca9debf56dd0d21762e537649dd92d9a4d

1 files changed, 82 insertions, 0 deletions

diff --git a/src/Subsampling/include/gudhi/pick_n_random_points.h b/src/Subsampling/include/gudhi/pick_n_random_points.h
new file mode 100644
index 00000000..4ca1fafc
--- /dev/null
+++ b/src/Subsampling/include/gudhi/pick_n_random_points.h
@@ -0,0 +1,82 @@
+/*    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_RANDOM_POINTS_H_
+#define PICK_RANDOM_POINTS_H_
+
+#include <boost/range/size.hpp>
+
+#include <random>     // random_device, mt19937
+#include <algorithm>  // shuffle
+#include <numeric>    // iota
+#include <iterator>
+#include <gudhi/Clock.h>
+
+
+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,
+                          unsigned final_size,
+                          OutputIterator output_it) {
+#ifdef GUDHI_SUBS_PROFILING
+    Gudhi::Clock t;
+#endif
+
+    unsigned nbP = boost::size(points);
+    assert(nbP >= final_size);
+    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
+  }
+
+} // namesapce subsampling
+  
+}  // namespace Gudhi
+
+#endif  // PICK_RANDOM_POINTS_H_