Racket Generic Graph Library: non-numerical edge weight/labels + Graphviz?

[unlimitedscolobb]

Hello,

I'm using the wonderful graph library which can do tons of various graph-related tasks.  However, I haven't found a way to attach non-numerical weights/labels to edges _and_ have them appear in the Graphviz rendering of the graph.

Is it at all possible?

I did see define-edge-property, but properties defined in this way do not appear in the Graphviz output.  I was looking for ways of passing edge properties to the graphviz function of the library, but there don't seem to be any.

I am planning to do a pull request enhancing the graphviz function with the possibility to include edge properties, but I wanted to ask around for some solutions which may already exist.

On a different note, I am somewhat surprised that the graph library enforces numerical edge weights at all.  I understand that some algorithms don't work if edges are not numbers, but on the other hand they could just fail gracefully on non-numerical edges.  Anyway, my best solution as of now would be extending graphviz, as this update would require modifying less code.

-

Sergiu

[Stephen Chang]

> I am somewhat surprised that the graph library enforces numerical edge weights at all.

The docs do informally say number weights but I don't think the
constructors do any checking? Any enforcement should be deferred to
individual algorithms.

Re: graphviz, I took a quick look and I think we could get the
behavior you want with a 1-line modification here, changing = to
equal?
https://github.com/stchang/graph/blob/master/graph-lib/graph/graph-fns-graphviz.rkt#L59-L60

Do you have an example I can work with?

I opened an issue so feel free to reply there instead:
https://github.com/stchang/graph/issues/53

On Sun, Feb 23, 2020 at 8:45 AM unlimitedscolobb
<unlimite...@gmail.com> wrote:
>
> Hello,
>
> I'm using the wonderful graph library which can do tons of various graph-related tasks. However, I haven't found a way to attach non-numerical weights/labels to edges _and_ have them appear in the Graphviz rendering of the graph.
>
> Is it at all possible?
>
> I did see define-edge-property, but properties defined in this way do not appear in the Graphviz output. I was looking for ways of passing edge properties to the graphviz function of the library, but there don't seem to be any.
>
> I am planning to do a pull request enhancing the graphviz function with the possibility to include edge properties, but I wanted to ask around for some solutions which may already exist.
>
>

> -
> Sergiu
>
> --
> You received this message because you are subscribed to the Google Groups "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to racket-users...@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/e4cb44fd-0a21-4e91-a75c-f1442127bfa9%40googlegroups.com.

[unlimitedscolobb]

Thank you very much for your answer Stephen!

I'll be busy the whole day tomorrow, but I'll come back in the evening most probably and will continue the discussion on the GitHub issue.

Indeed, I haven't seen the constructors actually check the edges to be numerical, but I had the impression that edge-weight had number? as the output contract:

  https://docs.racket-lang.org/graph/index.html#%28def._%28%28lib._graph%2Fmain..rkt%29._edge-weight%29%29

You are right: allowing non-numerical edges should be a matter of replacing a couple ='s with equal? and maybe generalising a contract or two.

I'll also give you an example in the discussion on the GitHub issue, in about 24 hours.

-

Sergiu

> To unsubscribe from this group and stop receiving emails from it, send an email to racket...@googlegroups.com.