StratifiedCrossValidationSplitting.cpp

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/*
 * 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.
 *
 * Written (W) 2011 Heiko Strathmann
 * Copyright (C) 2011 Berlin Institute of Technology and Max-Planck-Society
 */

#include <shogun/evaluation/StratifiedCrossValidationSplitting.h>
#include <shogun/features/Labels.h>
#include <shogun/lib/Set.h>

using namespace shogun;

CStratifiedCrossValidationSplitting::CStratifiedCrossValidationSplitting() :
    CSplittingStrategy(0, 0)
{
}

CStratifiedCrossValidationSplitting::CStratifiedCrossValidationSplitting(
        CLabels* labels, index_t num_subsets) :
    CSplittingStrategy(labels, num_subsets)
{
    build_subsets();
}

void CStratifiedCrossValidationSplitting::build_subsets()
{
    /* extract all labels */
    CSet<float64_t> unique_labels;
    for (index_t i=0; i<m_labels->get_num_labels(); ++i)
        unique_labels.add(m_labels->get_label(i));

    /* for every label, build set for indices */
    CDynamicObjectArray<CDynamicArray<index_t> > label_indices;
    for (index_t i=0; i<unique_labels.get_num_elements(); ++i)
        label_indices.append_element(new CDynamicArray<index_t> ());

    /* fill set with indices, for each label type ... */
    for (index_t i=0; i<unique_labels.get_num_elements(); ++i)
    {
        /* ... iterate over all labels and add indices with same label to set */
        for (index_t j=0; j<m_labels->get_num_labels(); ++j)
        {
            if (m_labels->get_label(j)==unique_labels[i])
            {
                CDynamicArray<index_t>* current=label_indices.get_element(i);
                current->append_element(j);
                SG_UNREF(current);
            }
        }
    }

    /* shuffle created label sets */
    for (index_t i=0; i<label_indices.get_num_elements(); ++i)
    {
        CDynamicArray<index_t>* current=label_indices.get_element(i);
        current->shuffle();
        SG_UNREF(current);
    }

    /* distribute labels to subsets for all label types */
    index_t target_set=0;
    for (index_t i=0; i<unique_labels.get_num_elements(); ++i)
    {
        /* current index set for current label */
        CDynamicArray<index_t>* current=label_indices.get_element(i);

        for (index_t j=0; j<current->get_num_elements(); ++j)
        {
            CDynamicArray<index_t>* next=m_subset_indices->get_element(
                    target_set++);
            next->append_element(current->get_element(j));
            target_set%=m_subset_indices->get_num_elements();
            SG_UNREF(next);
        }

        SG_UNREF(current);
    }

    /* finally shuffle to avoid that subsets with low indices have more
     * elements, which happens if the number of class labels is not equal to
     * the number of subsets */
    m_subset_indices->shuffle();
}