dlibs/dlib/clustering/chinese_whispers.h

// Copyright (C) 2012  Davis E. King ([email protected])
// 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_