[Matplotlib-users] subplots: common x and y labels

[Francesco M. <fra...@gm...>]

Dear matplolibers,

when dealing with multi-axes plot sometimes would be nice to use
figure-wide x and y labels.
On the web I've found some suggestion on how to do this, but I found
no solution valid in the general case and that integrate in the
matplotlib ecosystem.
The ideal would be to have a "set_xlabel" and "set_ylabel" method in the
Figure class, with the same api of the corresponding Axes methods.

As a proof of concept I've written a class derived from Figure , which
implements the two methods simply adding a horizontal (vertical) text below
(left of) the lowest (leftmost) axes.
The class together with a short example is attached.
I'm aware that the current implementation is really poor (no integration
with tight_layout, the padding must be adjusted by hand, a problem in
particular for the y label).

The best is to use "self.xaxis.set_label_text(xlabel, fontdict, **kwargs)"
as in the Axis set_xlabel (as I gather this create a label that is rendered
in the correct position accounting for ticklabels, ticks, tight_layout,
etc). To do this one would have to create:

   - a figure-wide invisible axes that encloses all the other
   axes/subplots, and whose dimension has to be updated every time a new
   axis/subplot is added (this should be easily done) with only the label
   visible. This could also allow to use axis features, like twin axis.
   - just the required axis (invisible) that hosts the labels. I think that
   this approach is less demanding computationally, but I don't know how much
   sense have two axis not attached to axes.

Any suggestions/hints on how to implement these methods in a better way is
very welcome.

If there is no opposition, later in the day I'll submit PR on github with
the two new method and see if we can get something out of this idea.

Cheers,
Francesco