How can I control within level node order in graphviz's dot?

Question

I have a graph that has a tree as its backbone. So I have, for example a node A with children B, C, and D. Assuming the graph is being drawn top-down, A will be on one level, then B, C, and D. I would like to force graphviz to lay them out in B, C, D order within their rank. Is this possible? If so, how?

If there are only A, B, C, and D, I can get this effect by just putting B, C, and D in that order in the input dot file. But if there are other edges out of B, C, and/or D, sometimes the order gets scrambled. That's what I would like to avoid.

Answer 1

This can be achieved with "invisible" edges as shown. Please note well the comments that describe how it works.

digraph test{

// make invisible ranks
rank1 [style=invisible];
rank2 [style=invisible];

// make "invisible" (white) link between them
rank1 -> rank2 [color=white];

// declare nodes all out of desired order
A -> D;
A -> B;
A -> C;
A -> E;

// even these new connection don't mess up the order
B -> F -> G;
C -> F -> G;

{
rank = same;
// Here you enforce the desired order with "invisible" edges and arrowheads
rank2 -> B -> C -> D -> E [ style=invis ];
rankdir = LR;
}
}

Answer 2

You don't need those magic rank1 and rank2.

Just:

1. Make the graph as usual.
2. Add nodes one again in a subgraph.

digraph test{

// declare nodes all out of desired order
A -> D;
A -> B;
A -> C;
A -> E;

B;C;D;E;

// even these new connection don't mess up the order
B -> F -> G;
C -> F -> G;

{
rank = same;
// Here you enforce the desired order with "invisible" edges and arrowheads
edge[ style=invis];
B -> C -> D -> E ;
rankdir = LR;
}
}

Answer 3

To help fill-out @TomServo's answer (for people struggling with "rank"), I've made the invisible edges visible:

Answer 4

I hit the same snag, and discovered the magic incantation is ordering=out

My full example looks like this:

digraph game_tree {
node [shape = circle, ordering=out];
f, h [shape=doublecircle, color=red];
k, n [shape=doublecircle, color=blue];
l, m [shape=doublecircle];
a -> b [label=1];
a -> c [label=2];
a -> d [label=3];
b -> e [label=4];
b -> f [label=5];
c -> g [label=4];
c -> h [label=5];
d -> i [label=4];
d -> j [label=5];
e -> k [label=6];
g -> l [label=6];
i -> m [label=7];
j -> n [label=8];
}