dlib C++ Library - feature_ranking_abstract.h

    // Copyright (C) 2008  Davis E. King (davisking@users.sourceforge.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_KERNEL_FEATURE_RANKINg_ABSTRACT_H_
    #ifdef DLIB_KERNEL_FEATURE_RANKINg_ABSTRACT_H_

    #include <vector>
    #include <limits>

    #include "svm_abstract.h"
    #include "kcentroid_abstract.h"
    #include "../is_kind.h"

    namespace dlib
    {

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

        template <
            typename kernel_type,
            typename sample_matrix_type,
            typename label_matrix_type
            >
        matrix<typename kernel_type::scalar_type> rank_features (
            const kcentroid<kernel_type>& kc,
            const sample_matrix_type& samples,
            const label_matrix_type& labels,
            const long num_features = samples(0).nr()
        );
        /*!
            requires
                - is_binary_classification_problem(samples, labels) == true
                - kc.train(samples(0)) must be a valid expression.  This means that
                  kc must use a kernel type that is capable of operating on the
                  contents of the samples matrix
                - 0 < num_features <= samples(0).nr()
            ensures
                - Let Class1 denote the centroid of all the samples with labels that are < 0
                - Let Class2 denote the centroid of all the samples with labels that are > 0
                - finds a ranking of the features where the best features come first.  This
                  function does this by computing the distance between the centroid of the Class1
                  samples and the Class2 samples in kernel defined feature space.
                  Good features are then ones that result in the biggest separation between
                  the two centroids of Class1 and Class2.
                - Uses the kc object to compute the centroids of the two classes
                - returns a ranking matrix R where:
                    - R.nr() == num_features
                    - r.nc() == 2
                    - R(i,0) == the index of the ith best feature according to our ranking.
                      (e.g. samples(n)(R(0,0)) is the best feature from sample(n) and
                       samples(n)(R(1,0)) is the second best, samples(n)(R(2,0)) the
                       third best and so on)
                    - R(i,1) == a number that indicates how much separation exists between
                      the two centroids when features 0 through i are used.
        !*/

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

    }

    #endif // DLIB_KERNEL_FEATURE_RANKINg_ABSTRACT_H_