How to make invisible nodes occupy space in graphviz?

Question

I want to plot a binary tree using graphviz, and it is important that the left child of a node appear to the left (duh) of the right child. If there is no left child, I want an empty space on the left, to make it visually clear that the right child is the right child. I want to do the same if there is no right child (on the right there should be an empty space).

For instance, I want something like:

A                     A
  \     instead of    |
    B                 B

I can make sure Graphviz will place the left child before the right by using ordering = "out", but if there is no left child, then the right child might appear right below its parent.

If I add dummy nodes where a child is missing, I get the correct layout, but the dummy nodes are then on the picture (and I don't want them). I tried using style = "invis" for the dummy nodes and edges connecting to them, but then it is as if they didn't exist for graphviz. How can I get around this problem?

Answer 1

Better late than never...

You probably left your dummy node empty (""). If you give it a reasonably sized label, it works fine:

graph Test 
{
    node[ shape = plaintext ];

    C [ label = "C", style = invis ];

    A -- B;
    A -- C [ style = invis ]; 
}

A good example to demonstrate that an MWE saves time and effort...