How to add edge labels in Graphviz?

Question

I am trying to draw a graph using Graphviz, but I need to add labels on the edges. There does not seem to be any way to that in Graphviz. Are there a way out?

Anthropocentric

Answer 1

You use the label property attached to the edge.

digraph G {
 a -> b [ label="a to b" ];
 b -> c [ label="another label"];
}

The above generates a graph that looks something like this.

Elson

Why are the labels touching the edges? Shouldn't there be a gap? – Acus

@Acus A quick fix is to just put a space at the beginning of the label: a -> b [ label=" a to b" ]; – Clingy

This duplicates the definitions a lot. Is there a way to do something like that: a - "a to b" > b - "b to c" > c ? – Underplay

Another fix is to use rankdir="LR";, which produces a horizontal graph with labels placed above the edge without touching. – Emmalynn

is there a way to have the labels rotated vertically to go paralle to the line? – Pash

I don't believe there's any need to declare a b or c before describing edges, is there? – Bismuthic

@Potherca Ha! Cool, I suppose, typically shouldn't edit other people's code, but in this case, probably fine. Good job, cheers! – Bismuthic

Regarding the labels touching the edges...the work-arounds mentioned seem a little ad-hoc, and also rely on axis aligned graph edges. Labels seem often to touch the edges with complex graphs. Is there no general solution? – Harebrained

For future reference, the DOT language documentation is here and the attributes documentation is here. – Appropriate

I wish the syntax was more like graph-easy: github.com/ironcamel/Graph-Easy/wiki#hello-world – Sidwel

Should we replace weight with label than? – Hammerless

Answer 2

@Andrew Walker has given a great answer!

It's also worth being aware of the labeltooltip attribute. This allows an additional string to be attached to the label of an edge. This is easier for a user than the tooltip attribute, as it can be fiddly to hover directly on an edge. The syntax is as follows:

digraph G {
 a -> b [label="  a to b" labeltooltip="this is a tooltip"];
 b -> c [label="  another label" ];
}

Which gives the following result:

Bigham

Tooltip hint invaluable. Thanks. – Bondwoman

Which version did you try with? With version dot - graphviz version 2.43.0 (0) tooltip does not show up. – Indian

Facing the same problem (using Graphviz Macport version 9.0.0 (20230911.1827)). – Rubious

Answer 3

Landed here by googling whether labels could be on arrow's ends, for UML's composition/aggregation. The answer is yes:

"Person" -> "Hand" [headlabel="*", taillabel="1"]

Roos

Answer 4

You can use label="\E" It will generate bye default label.

For Example:

digraph G {
 a -> b [ label="\E" ];
 b -> c [ label="\E"];
}

Meza