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c++boostgraphvizboost-graph

Boost.Graph and Graphviz nested subgraphs

I expected the code

#include <boost/graph/graphviz.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/subgraph.hpp>
#include <iostream>

using namespace boost;

using attrs_t = std::map<std::string, std::string>;

using graph_t = adjacency_list<
    vecS, vecS, directedS,
    property<vertex_attribute_t, attrs_t>,
    property<edge_index_t, int, property<edge_attribute_t, attrs_t>>,
    property<graph_name_t, std::string,
        property<graph_graph_attribute_t, attrs_t,
            property<graph_vertex_attribute_t, attrs_t,
                property<graph_edge_attribute_t, attrs_t>>>>>;

int main()
{
    char names[] = {"AB"};
    enum {A, B, N};

    subgraph<graph_t> main(N);
    subgraph<graph_t>& sub1 = main.create_subgraph();
    subgraph<graph_t>& sub2 = sub1.create_subgraph();

    add_vertex(A, sub1);
    add_vertex(B, sub2);
    add_edge(A, B, main);

    get_property(main, graph_name) = "G0";
    get_property(sub1, graph_name) = "clusterG1";
    get_property(sub2, graph_name) = "clusterG2";

    write_graphviz(std::cout, main, make_iterator_vertex_map(names));
}

to generate the graph on the left, whereas I have got the right one:

enter image description here

The output is:

digraph G0 {
subgraph clusterG1 {
subgraph clusterG2 {
//B;
}
//A;
}
A -> B;
}

The commented node statements are where the hierarchy information is lost (these lines I do not have in my output). How can I avoid that?

If I add both vertices into the same subgraph:

add_vertex(A, sub1);
add_vertex(B, sub1);
add_edge(A, B, main);

the connection A -> B appears in the scope of clusterG1 and from how I understand it, that is where the mentioned vertices will also be implicitly declared.

I am using Boost 1.68.0

Solution

  • Good spot. The linked answer actually has UB, as your own answer explains. The map passed in to the write_graphviz function isn't actually supposed to have the node_id for the graphviz output. Instead, that map was assumed to be a vertex_index_t propertymap.

    That was an assumption I probably held from boost::print_graph (graph_utility.hpp) that does that such property-map.

    To make it work safely I'd modify the example to employ write_graphviz_dp - using dynamic properties:

    int main() {
    boost::dynamic_properties dp;
    dp.property("node_id", boost::make_transform_value_property_map<std::string>(&name_for_index, boost::identity_property_map{}));
    write_graphviz_dp(std::cout, create_data<subgraph<Graph> >(), dp);
}

    I opted to use a transform function to get a name for any vertex descriptor, not wanting to assume anything about the number of vertices anymore either, I wrote the more general function to generate names like "A",...,"Z","AA",...,"ZZ" etc.:

    static std::string name_for_index(intmax_t index) {
    std::string name;

    do {
        name += 'A' + (index%26);
        index /= 26;
    } while (index);

    return name;
}

    Live On Coliru

    Retaining Subgraph Information

    The above overload doesn't have the subgraph support. So, instead let's fix the vertex_attribute map to have the expected vertex labels:

    int main() {
    auto g = create_data<subgraph<Graph> >();

    for (auto vd : make_iterator_range(vertices(g))) {
        put(get(vertex_attribute, g), vd, 
                GraphvizAttributes{
                    {"label", name_for_index(vd)}
                });
    }

    write_graphviz(std::cout, g);
}

    Now it does print:

    Live On Coliru

    digraph G0 {
subgraph clusterG1 {
graph [
label=G1];
node [
color=red, shape=Mrecord];
0[label="Vertex A"];
1[label="Vertex B"];
0 -> 1;
}
subgraph clusterG2 {
graph [
fillcolor=lightgray, label=G2, style=filled];
node [
shape=circle];
4[label="Vertex E"];
2[label="Vertex C"];
5[label="Vertex F"];
4 -> 5;
2 -> 5;
}
3[label="Vertex D"];
1 -> 2;
1 -> 3;
4 -> 1;
5 -> 3;
}

    Which renders as

    enter image description here

    Full Listing

    Preserving for posterity

    #include <boost/graph/graphviz.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/subgraph.hpp>
#include <iostream>

using namespace boost;

template <typename SubGraph> SubGraph create_data()
{
    enum { A,B,C,D,E,F,N }; // main edges
    SubGraph main(N);

    SubGraph& sub1 = main.create_subgraph();
    SubGraph& sub2 = main.create_subgraph();

    auto A1 = add_vertex(A, sub1);
    auto B1 = add_vertex(B, sub1);

    auto E2 = add_vertex(E, sub2);
    auto C2 = add_vertex(C, sub2);
    auto F2 = add_vertex(F, sub2);

    add_edge(A1, B1, sub1);
    add_edge(E2, F2, sub2);
    add_edge(C2, F2, sub2);

    add_edge(E, B, main);
    add_edge(B, C, main);
    add_edge(B, D, main);
    add_edge(F, D, main);

    // setting some graph viz attributes
    get_property(main, graph_name) = "G0";
    get_property(sub1, graph_name) = "clusterG1";
    get_property(sub2, graph_name) = "clusterG2";

    get_property(sub1, graph_graph_attribute)["label"]              = "G1";
    /*extra*/get_property(sub1, graph_vertex_attribute)["shape"]    = "Mrecord";

    get_property(sub2, graph_graph_attribute)["label"]              = "G2";
    /*extra*/get_property(sub1, graph_vertex_attribute)["color"]    = "red";
    /*extra*/get_property(sub2, graph_graph_attribute)["fillcolor"] = "lightgray";
    /*extra*/get_property(sub2, graph_graph_attribute)["style"]     = "filled";
    /*extra*/get_property(sub2, graph_vertex_attribute)["shape"]    = "circle";

    return main;
}

using GraphvizAttributes = 
    std::map<std::string, std::string>;

using Graph =
    adjacency_list<vecS, vecS, directedS, 
        property<vertex_attribute_t, GraphvizAttributes>,
        property<edge_index_t, int, property<edge_attribute_t, GraphvizAttributes> >,
        property<graph_name_t, std::string,
        property<graph_graph_attribute_t,  GraphvizAttributes,
        property<graph_vertex_attribute_t, GraphvizAttributes,
        property<graph_edge_attribute_t,   GraphvizAttributes>
        > > >
    >;

static std::string name_for_index(intmax_t index) {
    std::string name = "Vertex ";

    do {
        name += 'A' + (index%26);
        index /= 26;
    } while (index);

    return name;
}

int main() {
    auto g = create_data<subgraph<Graph> >();

    for (auto vd : make_iterator_range(vertices(g))) {
        put(get(vertex_attribute, g), vd, 
                GraphvizAttributes{
                    {"label", name_for_index(vd)}
                });
    }

    write_graphviz(std::cout, g);
}