MulticlassOneVsOneStrategy.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 Chiyuan Zhang
 * Copyright (C) 2012 Chiyuan Zhang
 */

#include <shogun/multiclass/MulticlassOneVsOneStrategy.h>
#include <shogun/labels/BinaryLabels.h>
#include <shogun/labels/MulticlassLabels.h>

using namespace shogun;

CMulticlassOneVsOneStrategy::CMulticlassOneVsOneStrategy()
    :CMulticlassStrategy(), m_num_machines(0)
{
}

void CMulticlassOneVsOneStrategy::train_start(CMulticlassLabels *orig_labels, CBinaryLabels *train_labels)
{
    CMulticlassStrategy::train_start(orig_labels, train_labels);
    m_num_machines=m_num_classes*(m_num_classes-1)/2;

    m_train_pair_idx_1 = 0;
    m_train_pair_idx_2 = 1;
}

bool CMulticlassOneVsOneStrategy::train_has_more()
{
    return m_train_iter < m_num_machines;
}

SGVector<int32_t> CMulticlassOneVsOneStrategy::train_prepare_next()
{
    CMulticlassStrategy::train_prepare_next();

    SGVector<int32_t> subset(m_orig_labels->get_num_labels());
    int32_t tot=0;
    for (int32_t k=0; k < m_orig_labels->get_num_labels(); ++k)
    {
        if (((CMulticlassLabels*) m_orig_labels)->get_int_label(k)==m_train_pair_idx_1)
        {
            ((CBinaryLabels*) m_train_labels)->set_label(k, +1.0);
            subset[tot]=k;
            tot++;
        }
        else if (((CMulticlassLabels*) m_orig_labels)->get_int_label(k)==m_train_pair_idx_2)
        {
            ((CBinaryLabels*) m_train_labels)->set_label(k, -1.0);
            subset[tot]=k;
            tot++;
        }
    }

    m_train_pair_idx_2++;
    if (m_train_pair_idx_2 >= m_num_classes)
    {
        m_train_pair_idx_1++;
        m_train_pair_idx_2=m_train_pair_idx_1+1;
    }

    subset.resize_vector(tot);
    return subset;
}

int32_t CMulticlassOneVsOneStrategy::decide_label(SGVector<float64_t> outputs)
{
    int32_t s=0;
    SGVector<int32_t> votes(m_num_classes);
    SGVector<int32_t> dec_vals(m_num_classes);
    votes.zero();
    dec_vals.zero();

    for (int32_t i=0; i<m_num_classes; i++)
    {
        for (int32_t j=i+1; j<m_num_classes; j++)
        {
            if (outputs[s]>0)
            {
                votes[i]++;
                dec_vals[i] += CMath::abs(outputs[s]);
            }
            else
            {
                votes[j]++;
                dec_vals[j] += CMath::abs(outputs[s]);
            }
            s++;
        }
    }

    int32_t i_max=0;
    int32_t vote_max=-1;
    float64_t dec_val_max=-1;

    for (int32_t i=0; i < m_num_classes; ++i)
    {
        if (votes[i] > vote_max)
        {
            i_max = i;
            vote_max = votes[i];
            dec_val_max = dec_vals[i];
        }
        else if (votes[i] == vote_max)
        {
            if (dec_vals[i] > dec_val_max)
            {
                i_max = i;
                dec_val_max = dec_vals[i];
            }
        }
    }

    return i_max;
}