CrossValidationSplitting.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) 2012 Heiko Strathmann
 * Copyright (C) 2012 Berlin Institute of Technology and Max-Planck-Society
 */

#include <shogun/evaluation/CrossValidationSplitting.h>
#include <shogun/labels/Labels.h>

using namespace shogun;

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

CCrossValidationSplitting::CCrossValidationSplitting(
        CLabels* labels, index_t num_subsets) :
    CSplittingStrategy(labels, num_subsets)
{
}

void CCrossValidationSplitting::build_subsets()
{
    /* ensure that subsets are empty and set flag to filled */
    reset_subsets();
    m_is_filled=true;

    /* permute indices */
    SGVector<index_t> indices(m_labels->get_num_labels());
    indices.range_fill();
    for (index_t i=0; i<indices.vlen; ++i)
    {
        CMath::swap(indices.vector[i],
                indices.vector[CMath::random(0, indices.vlen-1)]);
    }

    index_t num_subsets=m_subset_indices->get_num_elements();

    /* distribute indices to subsets */
    index_t current_subset=0;
    for (index_t i=0; i<indices.vlen; ++i)
    {
        /* fill current subset */
        CDynamicArray<index_t>* current=(CDynamicArray<index_t>*)
                m_subset_indices->get_element(current_subset);

        /* add element of current index */
        current->append_element(indices.vector[i]);

        /* unref */
        SG_UNREF(current);

        /* iterate over subsets */
        current_subset=(current_subset+1) % num_subsets;
    }

    /* 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();
}