Create a straight edge between nodes if there is another node branching from the midpoint of the edge in DiagrammeR?

Question

In DiagrammeR, I would like to pass a valid graph specification string in the DOT language to grViz() that will force a straight edge from node a0 to a1 when there is a separate edge branching off to b0. b0 will be larger than a0 so how do I align a0 and b0 on the same rank where the top of b0 is level with the top of a0?

Current graph specification:

library(DiagrammeR)
grViz("
  digraph G {
    
    node [shape=box];
    a0; a1;
    b0[height=1,width=2];
    node [shape = point, width = 0, height = 0];
    y1;
    
    a0 -> y1 [arrowhead=none];
    y1 -> a1;
    y1 -> b0;

    {rank=same; a0; b0;}
 
  }
")

Current output:

Desired output:

sroush · Accepted Answer · 2025-01-28 00:03:59Z

3

b0 is different size, so had to change to rankdir=LR to put b0 in its own (vertical) rank.
Then placed a0, a1 and y1 in their own rank

digraph G {
    rankdir=LR  // b0 is larger, so place in a different rank

    node [shape=box];
    {rank=same
      a0; a1;
      y1 [shape = point, width = 0, height = 0];
    }
    b0[height=1.5,width=2];
    
    a0 -> y1 [arrowhead=none];
    y1 -> a1;
    y1 -> b0; 
}

Giving:

answered Jan 28 at 0:03

sroush

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9 Comments

SRL Jan 28 at 1:25

If I want to add a1 -> {a2, a3}, how would I specify the layout so that these two additional boxes are displayed vertically below a1, but horizontally side by side?

Onyambu Jan 28 at 2:45

Wait. How do you run this code? In R?

sroush Jan 28 at 4:14

@Onyambu - this is a dot (Graphviz) (graphviz.org) program

sroush Jan 28 at 4:15

@SRL where do you want a2 & a3 in relationship to b0?

user20650 Jan 28 at 11:50

@Onyambu : given the tags likely the user is using DiagrammeR::grViz, but yes R and diagrammer are not relevant here to the question or answer. But at the same time many R users of these packages do not realise they are using graphviz. Also diagrammer does not offer complete graphviz correspondence, which sometimes can be relevant t the question.

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