pydata / pydata/xarray

get the same 'hue' behaviour in .quiver compared to the standard .plot()

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enhancement topic-plotting
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Python
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Description

Is your feature request related to a problem?

I have a 3 dimensions arrows, I would like to plot on top of each other.
I tried to use the usual hue attribute within xr.quiver, but it doesn't behave similarly to xr.plot(), where hue is used to unpack the extra dimension.

Below a minimal example of my issue:

import numpy as np
import xarray as xr
import matplotlib.pyplot as plt

x_size = 6; y_size = 4; w_size = 2
xv = np.arange(0,x_size)
yv = np.arange(0,y_size)
wv =  np.arange(0,w_size)
x, y, w = np.meshgrid(xv, yv, wv)
u = np.random.uniform(size=(y_size, x_size, w_size))
v = np.random.uniform(size=(y_size, x_size, w_size))

myds = xr.Dataset({
    'x': (['x'], xv),
    'y': (['y'], yv),
    'w': (['w'], wv),
    'u': (['y','x','w'], u),
    'v': (['y','x','w'], v),
})

If I unpack my data using col, it works fine:

myds.plot.quiver(x='x', y='y', u='u', v='v', col='w', 
                 scale=10, add_guide=False,)

Image

If I add the hue option, I got the colours as expected:

myds.plot.quiver(x='x', y='y', u='u', v='v', col='w', 
                 hue='w',
                 scale=10, add_guide=False,)

Image

but if I only use hue and not col, I get an error, because quiver doesn't unpack along the remaining dimension:

myds.plot.quiver(x='x', y='y', u='u', v='v', 
                 hue='w',
                 scale=10, add_guide=False,)

with the following error:

File /env/lib/python3.11/site-packages/matplotlib/quiver.py:420, in _parse_args(caller_name, *args)
    417 else:
    418     raise _api.nargs_error(caller_name, takes="from 2 to 5", given=nargs)
--> 420 nr, nc = (1, U.shape[0]) if U.ndim == 1 else U.shape
    422 if X is not None:
    423     X = X.ravel()

ValueError: too many values to unpack (expected 2)
Describe the solution you'd like

What I would expect is to have a behaviour similar to what we usually have with xr.plot, with automatic unpacking along the dimension with the hue option.

Describe alternatives you've considered

We can do it by reshaping the data, but we loose xarray simplicity.

xc = x.reshape((x_size, y_size * w_size))
yc = y.reshape((x_size, y_size * w_size))
wc = w.reshape((x_size, y_size * w_size))
uc = u.reshape((x_size, y_size * w_size))
vc = v.reshape((x_size, y_size * w_size))

plt.quiver(xc, yc, uc, vc, wc, scale=10)

Image

I tried to 'reshape' my xarray dataset with .stack, but I didn't find a suitable solution to work with xr.quiver.

Additional context

No response

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start at the xarray plot.quiver implementation and compare its hue handling with the standard xarray plot behavior; reproduce the provided Dataset example to trace the remaining-dimension error from matplotlib quiver. Done means hue alone automatically unpacks the extra dimension, applies the expected colors, and no longer raises the shown ValueError.

Written by the indexing model from the issue text.

Assessment

Tech stack
numpy, python
Domain
data-visualization
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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