source: trunk/c++_tools/classifier/CrossValidationSampler.cc @ 675

// $Id: CrossValidationSampler.cc 675 2006-10-10 12:08:45Z jari $

/*
  Copyright (C) 2006 Peter Johansson

  This file is part of the yat library, http://lev.thep.lu.se/trac/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 2 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 "yat/classifier/CrossValidationSampler.h"
#include "yat/classifier/Target.h"
#include "yat/random/random.h"

#include <algorithm>
#include <cassert>
#include <utility>
#include <vector>

namespace theplu {
namespace classifier {  

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

  CrossValidationSampler::~CrossValidationSampler()
  {
  }

  void CrossValidationSampler::build(const Target& target, size_t N, size_t k)
  {
    std::vector<std::pair<size_t,size_t> > v;
    for (size_t i=0; i<target.size(); i++)
      v.push_back(std::make_pair(target(i),i));
    // sorting with respect to class
    std::sort(v.begin(),v.end());
    
    // my_begin[i] is index of first sample of class i
    std::vector<size_t> my_begin;
    my_begin.reserve(target.nof_classes());
    my_begin.push_back(0);
    for (size_t i=1; i<target.size(); i++)
      while (v[i].first > my_begin.size()-1)
        my_begin.push_back(i);
    my_begin.push_back(target.size());

    random::DiscreteUniform rnd;

    for (size_t i=0; i<N; ) {
      // shuffle indices within class each class
      for (size_t j=0; j<target.nof_classes(); j++)
        random_shuffle(v.begin()+my_begin[j],v.begin()+my_begin[j+1],rnd);
      
      for (size_t part=0; part<k && i<N; i++, part++) {
        std::vector<size_t> training_index;
        std::vector<size_t> validation_index;
        for (size_t j=0; j<v.size(); j++) {
          if (j%k==part)
            validation_index.push_back(v[j].second);
          else
            training_index.push_back(v[j].second);
        }

        training_index_.push_back(training_index);
        validation_index_.push_back(validation_index);
      }
    }
    assert(training_index_.size()==N);
    assert(validation_index_.size()==N);
    
    for (size_t i=0; i<N; ++i){
      training_target_.push_back(Target(target,training_index_[i]));
      validation_target_.push_back(Target(target,validation_index_[i]));
    }
    assert(training_target_.size()==N);
    assert(validation_target_.size()==N);
  }

}} // of namespace classifier and namespace theplu