Ordering flowchart in graphviz

Question

The graph I'd like to produce is a something like this a left-to-right flowchart with a main process at the top, and a series of groupings of stuff below that feed in and out at various points like this: (though this is a dummy example and I want lots of stuff coming in and out from the top code box, which is why a horizontal layout works better than the default

The problem is that this is made in powerpoint...

I can get something close with this:

digraph example {
  
  graph [
    rankdir = LR
  ]
  
  subgraph cluster_code {
    label = "code";
    A;
    B;
    C;
    D;
  }

  subgraph cluster_data {
    label = "data";
    data_1;
    data_2;
  }
  
  subgraph cluster_source {
    label = "source"
    source_1;
    source_2
  }
  
   A -> B
   B -> C
   C -> D
  
  data_1 -> A
  data_2 -> B
  A -> output_1
  output_1 -> C
  
  source_1 -> data_1
  source_2 -> data_2
  
  #{rank = same; source_2; data_2; A}
  
}

But if I try to bring the source and data clusters underneath the code cluster using {rank = same; source_2; data_2; A} (this is hashed out above, and I don't repeat the whole code for brevity of the post), I then A, data_2 and source_2 drop out of the box. I think this is something do do with rank and clusters not playing nicely together.

Any hints on getting something like the first graph above?

Am running graphviz via R/Rstudio and DiagrammeR.

score 1 · Accepted Answer · answered Jan 19 '21 at 03:04

It seems that you want to change "rankdir" in the middle of the graph. Quite reasonable, but Graphviz doesn't support it. Here is your graph, using default rankdir and the not-that-well-documented ability to effectively change rankdir by using rank=same in a subgraph. It also reverses edge arrowhead direction - a kludge, but it works.

digraph example {
  node [width=1.5]

  subgraph cluster_code {
    label = "code";
    {rank=same 
    A -> B -> C -> D    
    }
  }

  subgraph cluster_data {
    label = "data";
    data_1;
    data_2;
  }
  
  subgraph cluster_source {
    label = "source"
    source_1;
    source_2
  }
  
  A -> output_1
  output_1 -> C
  
  edge[dir=back minlen=2]  // minlen makes (rank) space
  A -> data_1  // -> A
  A -> data_2  // -> A
  
  edge[dir=back minlen=1]
  data_1 -> source_1 // -> data_1
  data_2 -> source_2 // -> data_2
}

Giving this:

this needs to send the arrows backwards makes my head spin, but also makes perfect sense as to how you're gaming the mechanism - great solution — Scransom, Jan 19 '21 at 05:30

Ordering flowchart in graphviz

1 Answers1