Dataset.plot.quiver

[dcherian]

• Closes Add Dataset.plot.quiver #4373
• Tests added
• Passes isort . && black . && mypy . && flake8
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

I could use some help with adding tests and parameter checking if someone wants to help :)

import numpy as np
import xarray as xr

ds = xr.Dataset()
ds.coords["x"] = ("x", np.arange(10))
ds.coords["y"] = ("y", np.arange(20))
ds.coords["t"] = ("t", np.arange(4))
ds["u"] = np.sin((ds.x - 5) / 5) * np.sin((ds.y - 10) / 10)
ds["v"] = np.sin((ds.x - 5) / 5) * np.cos((ds.y - 10) / 10)

ds = ds * 2*np.cos((ds.t) * 2 * 3.14 /0.75)

ds["u"].attrs["units"] = "m/s"
ds["mag"] = np.hypot(ds.u, ds.v)

ds.mag.plot(col="t", x="x")

fg = ds.plot.quiver(x="x", y="y", u="u", v="v", col="t", hue="mag")

[dcherian]

This is ready for a review. I don't I can fix the quiverkey without matplotlib/matplotlib#18530 . This is still useful for a quick look at the data.

[mathause]

Looks good. The plotting code is not getting simpler 🙃 but it's so useful!

• Why is scale required for facetgrid and not for a single panel?
• Should it emit a Warning/ Error if u or v are given and funcname != "quiver"

[dcherian]

Why is scale required for facetgrid and not for a single panel?

matplotlib will make a nice choice for the single panel. With facetgrid, the scale will be different for each panel if we don't specify it. And i had trouble porting the matplotlib algorithm. We can always add this in the future.

Should it emit a Warning/ Error if u or v are given and funcname != "quiver"

Good idea. Done.

[dcherian]

technically backwards incompatible but I'm not sure it affects anyone.

[mathause]

Looks good (but I don't have experience with plt.quiver).

[dcherian]

I'll merge on Friday if there are no more comments.