dlib C++ Library - roc_trainer.h

    // Copyright (C) 2009  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_ROC_TRAINEr_H_
    #define DLIB_ROC_TRAINEr_H_

    #include "roc_trainer_abstract.h"
    #include "../algs.h"
    #include <limits>

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        template <
            typename trainer_type
            >
        class roc_trainer_type
        {
        public:
            typedef typename trainer_type::kernel_type kernel_type;
            typedef typename trainer_type::scalar_type scalar_type;
            typedef typename trainer_type::sample_type sample_type;
            typedef typename trainer_type::mem_manager_type mem_manager_type;
            typedef typename trainer_type::trained_function_type trained_function_type;

            roc_trainer_type (
            ) : desired_accuracy(0), class_selection(0){}

            roc_trainer_type (
                const trainer_type& trainer_,
                const scalar_type& desired_accuracy_,
                const scalar_type& class_selection_
            ) : trainer(trainer_), desired_accuracy(desired_accuracy_), class_selection(class_selection_)
            {
                // make sure requires clause is not broken
                DLIB_ASSERT(0 <= desired_accuracy && desired_accuracy <= 1 &&
                             (class_selection == -1 || class_selection == +1),
                            "\t roc_trainer_type::roc_trainer_type()"
                            << "\n\t invalid inputs were given to this function"
                            << "\n\t desired_accuracy: " << desired_accuracy
                            << "\n\t class_selection:  " << class_selection
                            );
            }

            template <
                typename in_sample_vector_type,
                typename in_scalar_vector_type
                >
            const trained_function_type train (
                const in_sample_vector_type& samples,
                const in_scalar_vector_type& labels
            ) const
            /*!
                requires
                    - is_binary_classification_problem(samples, labels) == true
            !*/
            {
                // make sure requires clause is not broken
                DLIB_ASSERT(is_binary_classification_problem(samples, labels),
                            "\t roc_trainer_type::train()"
                            << "\n\t invalid inputs were given to this function"
                            );

                return do_train(mat(samples), mat(labels));
            }

        private:

            template <
                typename in_sample_vector_type,
                typename in_scalar_vector_type
                >
            const trained_function_type do_train (
                const in_sample_vector_type& samples,
                const in_scalar_vector_type& labels
            ) const
            {
                trained_function_type df = trainer.train(samples, labels);

                // clear out the old bias
                df.b = 0;

                // obtain all the scores from the df using all the class_selection labeled samples
                std::vector<double> scores;
                for (long i = 0; i < samples.size(); ++i)
                {
                    if (labels(i) == class_selection)
                        scores.push_back(df(samples(i)));
                }

                if (class_selection == +1)
                    std::sort(scores.rbegin(), scores.rend());
                else
                    std::sort(scores.begin(), scores.end());

                // now pick out the index that gives us the desired accuracy with regards to selected class
                unsigned long idx = static_cast<unsigned long>(desired_accuracy*scores.size() + 0.5);
                if (idx >= scores.size())
                    idx = scores.size()-1;

                df.b = scores[idx];

                // In this case add a very small extra amount to the bias so that all the samples
                // with the class_selection label are classified correctly.
                if (desired_accuracy == 1)
                {
                    if (class_selection == +1)
                        df.b -= std::numeric_limits<scalar_type>::epsilon()*df.b;
                    else
                        df.b += std::numeric_limits<scalar_type>::epsilon()*df.b;
                }

                return df;
            }

            trainer_type trainer;
            scalar_type desired_accuracy;
            scalar_type class_selection;
        };

    // ----------------------------------------------------------------------------------------

        template <
            typename trainer_type
            >
        const roc_trainer_type<trainer_type> roc_c1_trainer (
            const trainer_type& trainer,
            const typename trainer_type::scalar_type& desired_accuracy
        ) { return roc_trainer_type<trainer_type>(trainer, desired_accuracy, +1); }

    // ----------------------------------------------------------------------------------------

        template <
            typename trainer_type
            >
        const roc_trainer_type<trainer_type> roc_c2_trainer (
            const trainer_type& trainer,
            const typename trainer_type::scalar_type& desired_accuracy
        ) { return roc_trainer_type<trainer_type>(trainer, desired_accuracy, -1); }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_ROC_TRAINEr_H_