Changes I'm not 100% sure about:

• Changed the ordinal scale to filter domain to unique values. The way it currently handles duplicates is not ideal since it will project values to the first instance of the value but generate a scale according to the count of all values including duplicates. Could also be fixed by changing the calculation of segments instead.
• Created a new base class for shapes generated by a CategorySeries. This is mostly to handle legends separately but also anything else that may come up. Feels weird creating a separate base class but maybe necessary and more explicit.
• CategoryShapes accept sequences as fill color. Need to add support for style_function input.
• Added a z axis, scale and type to Chart, and CategoryShapes have a legend_dimension property. This is to do a kind of merge between the category dimension and the 'sub-category' dimension (Y in the GroupedBars case, X in GroupedColumns). Category axes and scales replace the axes and scales in the legend_dimension and legends are created for the data in the legend_dimension.

That last point is probably the funkiest conceptual change I have to think about more.

I think this is super close. The ordinal stuff itches a little. I'll try to take a closer look this week.

Sounds good, I agree about ordinal stuff, also some color stuff I need to fix up. I'll add some adjustments in the next few days.

Happier with the code now but I'm not sure what to do about the ordinal scale's duplicate value handling.

Added GroupedColumns to make sure this set up would actually work well with different shapes/dimensions. It was pretty easy 👍. img link

Closing as stale PR.