cluster_leiden.hpp

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#ifndef SCRAN_GRAPH_CLUSTER_CLUSTER_LEIDEN_HPP
#define SCRAN_GRAPH_CLUSTER_CLUSTER_LEIDEN_HPP
 
#include <vector>
#include <algorithm>
 
#include "raiigraph/raiigraph.hpp"
#include "igraph.h"
 
namespace scran_graph_cluster {
 
struct ClusterLeidenOptions {
    double resolution = 1;
 
    double beta = 0.01;
 
    int iterations = 2;
 
    bool modularity = false;
 
    bool report_quality = true;
 
    int seed = 42;
};
 
struct ClusterLeidenResults {
    int status = 0;
    
    raiigraph::IntegerVector membership;
 
    igraph_real_t quality = 0;
};
 
inline void cluster_leiden(const igraph_t* graph, const igraph_vector_t* weights, const ClusterLeidenOptions& options, ClusterLeidenResults& output) {
    auto membership = output.membership.get();
    auto quality = (options.report_quality ? &(output.quality) : NULL);
 
    raiigraph::RNGScope rngs(options.seed);
 
    if (!options.modularity) {
        output.status = igraph_community_leiden(
            graph, 
            weights,
            NULL,
            options.resolution, 
            options.beta,
            false, 
            options.iterations, 
            membership, 
            NULL,
            quality
        );
 
    } else {
        // More-or-less translated from igraph::cluster_leiden in the R package.
        raiigraph::RealVector strengths(igraph_vcount(graph));
        igraph_strength(graph, strengths, igraph_vss_all(), IGRAPH_ALL, 1, weights);
 
        double total_weights = igraph_vector_sum(strengths);
        double mod_resolution = options.resolution / total_weights;
 
        output.status = igraph_community_leiden(
            graph, 
            weights, 
            strengths, 
            mod_resolution, 
            options.beta, 
            false, 
            options.iterations, 
            membership, 
            NULL, 
            quality
        );
    }
}
 
inline ClusterLeidenResults cluster_leiden(const raiigraph::Graph& graph, const std::vector<igraph_real_t>& weights, const ClusterLeidenOptions& options) {
    // No need to free this, as it's just a view.
    igraph_vector_t weight_view;
    igraph_vector_view(&weight_view, weights.data(), weights.size());
 
    ClusterLeidenResults output;
    cluster_leiden(graph.get(), &weight_view, options, output);
    return output;
}
 
}
 
#endif