source: trunk/yat/classifier/BootstrapSampler.cc @ 1486

// $Id: BootstrapSampler.cc 1486 2008-09-09 21:17:19Z jari $

/*
  Copyright (C) 2007 Jari Häkkinen, Peter Johansson
  Copyright (C) 2008 Peter Johansson

  This file is part of the yat library, http://dev.thep.lu.se/yat

  The yat library 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.

  The yat library 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, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  02111-1307, USA.
*/

#include "BootstrapSampler.h"
#include "Target.h"
#include "yat/random/random.h"

#include <cassert>

namespace theplu {
namespace yat {
namespace classifier {  

  BootstrapSampler::BootstrapSampler(const Target& target, size_t N)
    : Sampler(target, N)
  { 
    assert(target.size()>1);
    build(target, N);
  }

  BootstrapSampler::~BootstrapSampler()
  {
  }

  void BootstrapSampler::build(const Target& target, size_t N)
  {
    // index[i] gives all indices that belong to class i 
    std::vector<std::vector<size_t> > index(target.nof_classes());

    for (size_t i = 0; i<target.size(); ++i)
      index[target(i)].push_back(i);

    random::DiscreteUniform rnd;

    for (size_t i = 0; i<N; ++i){
      std::vector<size_t> training_index;
      std::vector<size_t> validation_index;
      training_index.reserve(target.size());
      validation_index.reserve(target.size());
      
      for (size_t label=0; label<target.nof_classes(); ++label) {
        std::vector<char> drawn(index[label].size(),0);
        for (size_t j=0; j<index[label].size(); ++j) {
          size_t k = rnd(index[label].size());
          training_index.push_back(index[label][k]);
          drawn[k]=1;
        }
        for (size_t j=0; j<index[label].size(); ++j)
          if (!drawn[j]) {
            validation_index.push_back(index[label][j]);
          }
      }
      training_index_.push_back(utility::Index(training_index));
      training_target_.push_back(Target(target,utility::Index(training_index)));
      validation_index_.push_back(utility::Index(validation_index));
      validation_target_.push_back(Target(target,
                                          utility::Index(validation_index)));
    }

  }

}}} // of namespace classifier, yat, and theplu