Extracting Layers and Subgraph Clusters from Graphviz with gvpr

Question

I have a large Graphviz file where I have put different nodes and edges onto different layers. A number of nodes are grouped into a subgraph cluster.

This makes it easy to focus on the particular part of the graph that is important. However I would now like to extract each layer into its own DOT file automatically.

I've been using gvpr -i 'N[layer=="(*a*)"]' source.gv > a.gv, which achieves what I want, by extracting the nodes and edges, but it fails to extract the subgraph, so I lose the context of the nodes.

For example, with the source graph:

digraph {
    layers = "a:b";
    layerselect = "";

    subgraph cluster_alpha {
        label = "Alpha";
        a, b, c [layer = "a"];
    }

    subgraph cluster_beta {
        label = "Beta";
        d, e, f [layer = "b"];
    }

    g [layer = "a"];
    h [layer = "b"];

    g -> a [layer = "a"];
    h -> e [layer = "b"]
}

Running gvpr -i 'N[layer=="(*a*)"]' source.gv > a.gv results in the following output:

digraph gvpr_result {
    graph [layers="a:b:c",
        layerselect=""
    ];
    a    [layer=a];
    b    [layer=a];
    c    [layer=a];
    g    [layer=a];
    g -> a   [layer=a];
}

If you compare the output you will see that the box around nodes "a", "b", and "c" and the label "Alpha" is missing.

Do you have any suggestions on how I can use gvpr to also output the subgraph clusters, or some other strategy to output the nodes, edges, and subgraphs of a given layer to a DOT file?

Ottillia

Answer 1

What you want needs a bit more code. Call this file source.gvpr:

BEG_G
 {
  int i;
  int found;
  graph_t subgraphs[int];
  graph_t subgraph;
  subgraph = fstsubg($);
  i = 0;
  while (subgraph != NULL)
   {
    if (substr(subgraph.name, 0, 1) != "%")
     {
      subgraphs[i++] = subgraph;
     }
    subgraph = nxtsubg(subgraph);
   }
 }

N[layer=="(*a*)"]
 {
  found = 0;
  for (i = 0; i < #subgraphs; ++i)
   {
    if (isSubnode(subgraphs[i], $))
     {
      graph_t sg = subg($T, subgraphs[i].name);
      copyA(subgraphs[i], sg);
      subnode(sg, $);
      ++found;
      break;
     }
   }
  if (found  == 0)
   {
    node_t newnode = node($T, $.name);
    copyA($, newnode);
   }
 }

E[layer=="(*a*)"]

Run it with:

gvpr -f source.gvpr source.gv -o a.gv

The result will hopefully be what you wanted:

digraph gvpr_result {
  graph [layers="a:b",
    layerselect=""
  ];
  subgraph cluster_alpha {
    graph [label=Alpha,
      layers="a:b"
    ];
    a    [layer=a];
    b    [layer=a];
    c    [layer=a];
  }
  g  [layer=a];
  g -> a   [layer=a];
}

I am working on a version for myself that allows the selection of wanted layers via command line arguments (-a) of gvpr. Also it looks like a separate layer is required for edges that connect nodes of different layers if you want them to vanish when only one of such layers is chosen.

Lippi

Did you get the CLI-enabled version working? – Atomism