inverted_index.hpp

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#pragma once

#include <search/search_base/search_base.hpp>
#include <search/bag_of_words/bag_of_words.hpp>

/// Implements a Bag of Words based (BoW) image search using an inverted index.  The inverted
/// index keeps track of a list of images associated with each visual word.  The images are
/// represented as an unsigned long long which must then be translated back to an actual image
/// using the appropriate Dataset class implementation.
class InvertedIndex : public SearchBase {
public:

        /// Subclass of train params base which specifies inverted index training parameters.
        struct TrainParams : public TrainParamsBase {
                std::shared_ptr<BagOfWords> bag_of_words;  /// bag of words to index on
        };

        /// Subclass of train params base which specifies inverted index training parameters.
        struct SearchParams : public SearchParamsBase {
                
        };

        /// Subclass of match results base which also returns scores
        struct MatchResults : public MatchResultsBase {
                std::vector<float> tfidf_scores;
        };

        InvertedIndex();
        InvertedIndex(const std::string &file_name);

        /// Given a set of training parameters, list of images, trains.  Returns true if successful, false
        /// if not successful.
        bool train(Dataset &dataset, const std::shared_ptr<const TrainParamsBase> &params,
                                const std::vector< std::shared_ptr<const Image > > &examples);

        /// Loads a trained search structure from the input filepath
        bool load (const std::string &file_path);

        /// Saves a trained search structure to the input filepath
        bool save (const std::string &file_path) const;

        /// Returns the number of clusters used in the inverted index descriptors
        uint32_t num_clusters() const;

        /// Given a set of search parameters, a query image, searches for matching images and returns the match.  If the match is nullptr, then the search failed 
        /// (it will fail if the example image has missing features).
        std::shared_ptr<MatchResultsBase> search(Dataset &dataset, const std::shared_ptr<const SearchParamsBase> &params, const std::shared_ptr<const Image > &example);

protected:
        
        std::vector< std::vector<uint64_t> > inverted_index; /// Stores the inverted index, dimension one is the cluster index, dimension two holds a list of ids containing that word.
        std::vector<float> idf_weights; /// Stores the idf weights, one element per cluster

};

/// Prints out information about the match results.
std::ostream& operator<< (std::ostream &out, const InvertedIndex::MatchResults &match_results);