[Question] Is it possible to attach a unique label to a vertex

[ducky427]

Hi,
Thanks for this library. It looks really interesting and powerful.

I am looking at the spreadsheet example and trying to understand the vertex collection functions. By the looks of it, (f/signal-map v) returns a map of type {<id> value ...}, where <id> is the vertex number in the graph.

Is it possible to change that <id> into something user specified, so that the end user can reason about which value is associated with which node without trying to look it up in the graph.

I hope this makes sense.

cheers

[ducky427]

I can work around this issue by keeping a map of {<vertex-id> <my-id>...}. But it'll be nice to have that support as part of the graph.

[postspectacular]

Hiya, thanks for your interest & a good question. Custom vertex IDs are supported, but not exactly as what you're after...

1. when you create a new compute-graph, you can specify an ::id-gen-fn option. This is a single-arg function (taking nil or the previous ID) and produces the next vertex ID. By default this is simply a counter, but you could e.g. use this to generate UUIDs as vertex IDs:

(require '[thi.ng.fabric.core :as f])

(defn random-uuid (fn [_] (java.util.UUID/randomUUID)))

(def g (f/compute-graph {::f/id-gen-fn random-uuid}))

This however doesn't directly do what you asked for and I guess this is something which could be refactored (but would have to be supplied at construction time and couldn't be changed afterwards).

2. The other solution is to just add a custom a user field to each vertex:

(def VAT (f/add-vertex! g 1.2 {:cell-id :vat-rate}))

Then to obtain that (e.g. inside a collection function, whilst processing the signal map):

(->> sig-id (f/vertex-for-id g) f/state :cell-id)

Does this help?

[ducky427]

Thanks a lot for your response.

In the local context, for example inside a collection function, I think approach 2) would definitely work to get a mapping from vertex-id to :cell-id as you know the former.

In the longer term, I think I think vspec could probably be checked if it has a key called :id (or something) and only use ::next-id if it is not present.

This would also really help the end user in introspecting the values of the vertices in a large enough graph.

Thanks again.

[postspectacular]

That's a great idea and I will refactor this asap... would also be faster to acess during processing, but would too need to include a check that the user specified ID is unique during construction. cheers!

[ducky427]

Thanks a lot!