Give ArrayInterface lower priority

The ArrayInterface represents the original format for all our charts types, and it’s limitations are what made us eventually go down the route of interfaces (via the terrible diversion of NdElement). While it is a fairly straightforward format simply representing the Rows and Columns of your data as an array, it only works if your data is of uniform type. This means that you have to reason about the types of your data to know how HoloViews will store it. Therefore I’d argue it should not be the default datatype, letting us promote the PandasInterface and DictionaryInterface ahead of it. This means that for columnar data you will always be guaranteed to get one of those types on your .data attribute depending on whether you have pandas installed or not.

The only complication in making this change is that our testing machinery seemingly like neither pandas nor the dictionary data output, so wherever we print .data in the tutorials it fails to do the comparison correctly.

[philippjfr]

I’m going to push for this to be included in v1.10. It’s long overdue and have long recommended that users do not access .data directly.

[jlstevens]

I agree this is overdue.