Dear BGL users, I am trying to produce a simple routine to extract the subgraph of a graph, by using the vertex names of the subgraphs. That is, for two graphs G and H, I want to define the following operator: G -= H; Here, the resulting subgraph of G should have all the vertices that H doesn't have. During this process, the incident edges of the removed vertices are also removed. I have checked the subgraph class in BGL, but this refers to a substantially different concept. I have tried the following code, which works, but is extremely slow for the type of application that I had in mind: ////////////////////////////////////////////////// class Graph { public: typedef adjacency_list<vecS, vecS, undirectedS, property<vertex_name_t,int> > UndirectedGraph; Graph(); ~Graph(); int Nv(); // Return number of vertices Rcpp::IntegerVector V(); // Return vector of NAMES of vertices as integers. Graph& operator-= (Graph& H); private: UndirectedGraph G; }; ///////////////////////////////////////////////////////////////////////// // Overloaded Operators. Graph& Graph::operator-= (Graph& H){ typedef graph_traits<UndirectedGraph>::vertex_descriptor Vdescriptor; typedef property_map<UndirectedGraph,vertex_name_t>::type VertexNameMap; typedef iterator_property_map <int*, identity_property_map> name_to_vertex_map; Rcpp::IntegerVector vec = H.V(); VertexNameMap NameIndex; for(ivIter t=vec.begin(); t!=vec.end(); ++t){ // Create/Update Iterator map (LValuePropertyMap). int x[this->Nv()]; NameIndex = get(vertex_name,G); for(int i=0; i < this->Nv(); ++i) x[NameIndex[i]]=i; name_to_vertex_map NVmap(x); // Remove vertex from name of *t in H. Vdescriptor u=NVmap[*t]; clear_vertex(u,G); remove_vertex(u,G); }//t return *this; }//-= ////////////////////////////////////////////////// The problem seems to be that I re-create an iterator map (from vertex NAMES to vertex INDICES) every time I remove a single vertex. This seems counter-efficient. I would need to be able to create a reference to a similar map that is automatically updated every time I remove a vertex. However, since vertices in BGL are indexed from 0 to Nv-1, I don't see a way to produce a LValuePropertyMap from vertex's names to vertex's indices. Any help/opinion would be greatly appreciated, -- Cedric Ginestet Centre for Neuroimaging Sciences (L3.04) NIHR Biomedical Research Centre Department of Neuroimaging Institute of Psychiatry, Box P089 King's College London De Crespigny Park London SE5 8AF