Altair: Compatibility with / export to Matplotlib

[choldgraf]

This is a super promising library and I really like the simplified syntax for making basic chart types. However, a big bottleneck for me is that I still rely heavily on matplotlib for making final figures etc. I don't see that changing any time soon so I wonder if any thought has been put into connecting Altair with Matplotlib. Are there any plans in the works to create MPL figures etc using the vega-style specification? Or exporting Altair figures to matplotlib objects?

Perhaps this is also relevant to bring up on the MPL repo as well, but more generally would this be a long-term high-effort project, or something more doable in the short term?

[jakevdp]

Hi @choldgraf – it turns out if you dig into the very early commits in altair, we did have the beginnings of a matplotlib renderer for early versions of Vega-Lite specifications (See e.g. this file) Long-term it would be great to revisit this. I think it would be straightforward to render the most common pieces of the spec with matplotlib, but getting to 100% schema support would be a pretty substantial effort.

[jakevdp]

I'd be happy to see work in this area, but I probably won't be able to tackle it myself any time soon!

[choldgraf]

Yeah to me it kind of seems this would be more of a "trickle" feature than an all-at-once kind of thing (e.g. "Altair now supports exporting scatterplots to matplotlib"). I think it'd be a good test-case for what it'd actually look like if the vega-lite spec was a universal plotting spec.

Maybe I can play around with this in the coming months...just gauging interest and importance from you guys now :)

[jakevdp]

Eventually I'd love this to live in a separate package under the altair-viz organization. If you get a prototype working, please let us know!

[choldgraf]

ya I think that's a good idea too. I'll keep you updated if I start working on anything - want me to keep this issue open?

[jakevdp]

Yes, let's keep it open

[kanitw]

@choldgraf Yeah I think it would be exciting to see this happening.

Btw, it's worth noting that we (VL team) are working on Vega-Lite 2.0, which means there might be some breaking syntax change due to changes in Vega 3 and D3 4.0.

That said, I think it's probably doesn't hurt to start hacking a prototype. But of course it's definitely worth waiting before doing a full-blown Altair/VL to matplotlib compiler.

[jakevdp]

I've started a repo at http://github.com/altair-viz/altair_matplotlib

Not a lot there yet... and it turned out the old code wasn't really salvageable given the changes to Altair since then.

[jakevdp]

Note that the 2018 John Hunter Fellowship will support work on a matplotlib renderer for Altair/Vega-Lite! https://www.numfocus.org/programs/john-hunter-technology-fellowship

[samuelsinayoko]

Has there been any further work on this? Really like the idea of using Vega-Lite as a common language layer for the many Python visualization packages, starting with Matplotlib!