Hello Annie,
By numerical aspect, do you mean the range of the domain, and you'd like to get back the coded values? Could you describe a little bit more about your use case? I'm happy to look into it and see if we either have a way to work with the full domain information, or create an issue for this.
For the time being, a possible workaround would be to use the DomainToTable tool to convert the domain data in question into a table. You could do so in a Modelbuilder model, then feed the resulting table in as an input to your R tool, where you could interact with it like any other table (using arc.open + arc.select).
Cheers,
Shaun
