issue_comments

For those interested in this topic, see https://github.com/SciTools/nc-time-axis/pull/42.

I'll also note that @philippjfr has already added support for plotting cftime types in holoviews, https://github.com/ioam/holoviews/pull/2728, making use of the nc_time_axis.CalendarDateTime object in its matplotlib backend.

Thanks @pelson, that's good to hear that you would be open to someone doing some refactoring in nc-time-axis.

@rabernat @aidanheerdegen @jbusecke I think the cleanest approach for someone interested in fixing the built-in plotting issue then would be to engage with the nc-time-axis folks to see if there is a way to enable plotting with cftime.datetime objects directly (that they would feel comfortable with). Then in xarray, modulo some logic to handle the optional imports of cftime and nc_time_axis, I think it could just be a matter of adding cftime.datetime as one of the allowed types for plotting (within here), adding some tests, and maybe a documentation example.

I think a quick and dirty fix could be to add nc-time-axis as an optional dependency, and convert any cftime.datetime objects encountered in plotting routines to nc_time_axis.CalendarDateTime objects before passing them to matplotlib.

But I wonder if there is potentially room for improvement upstream in cftime? Should we need to convert to these proxy objects before plotting or might there be a way to make cftime objects themselves more friendly to use with matplotlib? That could have benefits for multiple libraries (not just xarray).

@pelson @lbdreyer @ocefpaf (developers of nc-time-axis and Iris) -- it seems you have grappled with this problem a fair bit already. Have you thought about those questions before?

@jbusecke I recently stumbled upon https://github.com/SciTools/nc-time-axis. You can install it through conda-forge: $ conda install -c conda-forge nc-time-axis However, for now you won't be able to use xarray's built in plotting, since xarray will raise an error if you try to plot anything with coordinates that aren't numeric or of type datetime.datetime or np.datetime64 (but nc-time-axis at least gives you matplotlib support). You'll also need to convert your dates to nc_time_axis.CalendarDateTime objects; you can do that with a simple list comprehension (see the example in their README).

I agree it would be very nice to enable plotting data with cftime.datetime coordinates with holoviews. Eventually it would also be great if we could enable it for xarray's built-in plotting too. I'm happy to help out where I can.