Number of DataRoles added

Hello, hoping someone could help.

Have created a custom vis and have set a dataRole that will take a minimum of 1 and maximum of 2 inputs.

I am wanting to have my R script change depending on whether I have 1 or 2 inputs. How can I access the dataRoles to check how many are there?

Or is there something I can add to an if statement in R to check how many inputs there are?

Thanks in advance!

Matt