Pyramid / back-to-back / symmetrical charts

As mentioned in #1836, I’d love to see a flag on Bar to switch the vertical axis to be the categorical axis so we can make charts like

(source: http://www.economist.com/news/21631911-end-population-pyramid-world-reshaped)

Am thinking it’s fairly easy code, but the interface could get confusing - at the moment my best suggestion would be vertical_cat (optional Bool that defaults to false). The reason this is weird is that then you can set a custom y_range, but it would actually be a custom x_range…suggestions welcome.

In implementing this would it be ok to add it as an example in the examples folder, or are there processes for adding new examples?

[birdsarah]

So, I’ve caused some confusion 😒

@bryevdv and @pzwang wrote some comments on #1851 about how to do a range (split / two-way / symmetric ) that would facilitate a pyramid plot.

It’s interesting, because I wasn’t imagining doing pyramid plots like that. To my mind, a pyramid plot is two bar charts back-to-back. And so I was just imagining sticking two seperate plots together.

See my ipython notebook - http://nbviewer.ipython.org/github/birdsarah/bokeh/blob/pyramid_plot/examples/plotting/notebook/pyramid_plot.ipynb:

• I’m pretty happy with the results using the low-level interface, I’m not sure why I’d want to implement a new range type.
• When I try to use the Bar charting interface, I’m almost there, but there are a couple of additional interfaces I need
  • ability to switch the categorical / linear axis - the original intention of this issue
  • now i’ve tried it I see I also need an interface to not add a categorical axis on one of the plots.

Maybe there are some different things bubbling here:

• Bar
• VerticalBar (where the vertical axis is categorical, and the horizontal linear)
• BackToBack (a generic interface to stick together two charts in mirror-image format)

[bryevdv]

There’s not a canned high level chart type for it, but you can certainly draw this type of chart, as demonstrated above. Now with hbar it should be even easier.