dlib C++ Library - chinese_whispers.h

    // Copyright (C) 2012  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_CHINESE_WHISPErS_Hh_
    #define DLIB_CHINESE_WHISPErS_Hh_

    #include "chinese_whispers_abstract.h"
    #include <vector>
    #include "../rand.h"
    #include "../graph_utils/edge_list_graphs.h"

    namespace dlib
    {

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

        inline unsigned long chinese_whispers (
            const std::vector<ordered_sample_pair>& edges,
            std::vector<unsigned long>& labels,
            const unsigned long num_iterations,
            dlib::rand& rnd
        )
        {
            // make sure requires clause is not broken
            DLIB_ASSERT(is_ordered_by_index(edges),
                        "\t unsigned long chinese_whispers()"
                        << "\n\t Invalid inputs were given to this function"
            );

            labels.clear();
            if (edges.size() == 0)
                return 0;

            std::vector<std::pair<unsigned long, unsigned long> > neighbors;
            find_neighbor_ranges(edges, neighbors);

            // Initialize the labels, each node gets a different label.
            labels.resize(neighbors.size());
            for (unsigned long i = 0; i < labels.size(); ++i)
                labels[i] = i;

            for (unsigned long iter = 0; iter < neighbors.size()*num_iterations; ++iter)
            {
                // Pick a random node.
                const unsigned long idx = rnd.get_random_64bit_number()%neighbors.size();

                // Count how many times each label happens amongst our neighbors.
                std::map<unsigned long, double> labels_to_counts;
                const unsigned long end = neighbors[idx].second;
                for (unsigned long i = neighbors[idx].first; i != end; ++i)
                {
                    labels_to_counts[labels[edges[i].index2()]] += edges[i].distance();
                }

                // find the most common label
                std::map<unsigned long, double>::iterator i;
                double best_score = -std::numeric_limits<double>::infinity();
                unsigned long best_label = labels[idx];
                for (i = labels_to_counts.begin(); i != labels_to_counts.end(); ++i)
                {
                    if (i->second > best_score)
                    {
                        best_score = i->second;
                        best_label = i->first;
                    }
                }

                labels[idx] = best_label;
            }

            // Remap the labels into a contiguous range.  First we find the
            // mapping.
            std::map<unsigned long,unsigned long> label_remap;
            for (unsigned long i = 0; i < labels.size(); ++i)
            {
                const unsigned long next_id = label_remap.size();
                if (label_remap.count(labels[i]) == 0)
                    label_remap[labels[i]] = next_id;
            }
            // now apply the mapping to all the labels.
            for (unsigned long i = 0; i < labels.size(); ++i)
            {
                labels[i] = label_remap[labels[i]];
            }

            return label_remap.size();
        }

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

        inline unsigned long chinese_whispers (
            const std::vector<sample_pair>& edges,
            std::vector<unsigned long>& labels,
            const unsigned long num_iterations,
            dlib::rand& rnd
        )
        {
            std::vector<ordered_sample_pair> oedges;
            convert_unordered_to_ordered(edges, oedges);
            std::sort(oedges.begin(), oedges.end(), &order_by_index<ordered_sample_pair>);

            return chinese_whispers(oedges, labels, num_iterations, rnd);
        }

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

        inline unsigned long chinese_whispers (
            const std::vector<sample_pair>& edges,
            std::vector<unsigned long>& labels,
            const unsigned long num_iterations = 100
        )
        {
            dlib::rand rnd;
            return chinese_whispers(edges, labels, num_iterations, rnd);
        }

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

        inline unsigned long chinese_whispers (
            const std::vector<ordered_sample_pair>& edges,
            std::vector<unsigned long>& labels,
            const unsigned long num_iterations = 100
        )
        {
            dlib::rand rnd;
            return chinese_whispers(edges, labels, num_iterations, rnd);
        }

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

    }

    #endif // DLIB_CHINESE_WHISPErS_Hh_