Group By variables in Platform Analytics

[scoburn1]

Hi All,

Is there any explicit documentation stating exactly what Request Item variable types are available to use as a Group By in Platform Analytics? 

With 'List - Simple' we seem to be able to access all variable types. However, with other visualizations such as Horizontal/Vertical bar and chart types, reference type variables appear to no longer be available. This was functionality that worked in the normal reporting module with no issue.

I've attached some screenshots of an example. I'm also referring to this documentation here:
https://www.servicenow.com/docs/bundle/yokohama-now-intelligence/page/use/reporting/concept/dv-rep-s...

To be clear, it looks like *some* variables can be used for chart types. Curious if anyone else has run into this or if we need to direct our users to change all their variable grouping reports to lists.