Closed
Description
Bug report
Bug summary
The streamplot method works on empty (fully masked or np.nan) or nearly empty (too few data points to plot a single streamline) array (for the u and v velocity arguments), unless color mapping is used by providing a 2D array as color= keyword argument.
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
# prepare fake data
x = y = np.arange(3)
u = v = np.arange(9).reshape(3, 3)
color = (u**2+v**2)**0.5
# streamplot without color mapping
plt.streamplot(x, y, u, np.ma.masked_greater(v, 4)) # works
plt.streamplot(x, y, u, np.ma.masked_greater(v, 3)) # works
plt.streamplot(x, y, u, np.ma.masked_all_like(v)) # works
plt.streamplot(x, y, u, v*np.nan) # works
# streamplot with color mapping
plt.streamplot(x, y, u, np.ma.masked_greater(v, 4), color=color) # works
plt.streamplot(x, y, u, np.ma.masked_greater(v, 3), color=color) # fails
plt.streamplot(x, y, u, np.ma.masked_all_like(v), color=color) # fails
plt.streamplot(x, y, u, v*np.nan, color=color) # failsActual outcome
Traceback (most recent call last):
File "/home/julien/emptystreamplot.py", line 19, in <module>
plt.streamplot(x, y, u, np.ma.masked_greater(v, 3), color=color) # fails
File "/usr/lib/python3.9/site-packages/matplotlib/pyplot.py", line 2978, in streamplot
__ret = gca().streamplot(
File "/usr/lib/python3.9/site-packages/matplotlib/__init__.py", line 1447, in inner
return func(ax, *map(sanitize_sequence, args), **kwargs)
File "/usr/lib/python3.9/site-packages/matplotlib/streamplot.py", line 222, in streamplot
lc.set_array(np.ma.hstack(line_colors))
File "/usr/lib/python3.9/site-packages/numpy/ma/extras.py", line 296, in __call__
_d = func(tuple([np.asarray(a) for a in x]), *args, **params)
File "<__array_function__ internals>", line 5, in hstack
File "/usr/lib/python3.9/site-packages/numpy/core/shape_base.py", line 346, in hstack
return _nx.concatenate(arrs, 1)
File "<__array_function__ internals>", line 5, in concatenate
ValueError: need at least one array to concatenate
Expected outcome
Because other plotting methods work on empty arrays, I expect streamplot to handle the above case (and draw nothing).
Matplotlib version
- Operating system: Manjaro Linux
- Matplotlib version: 3.3.3
- Matplotlib backend: Qt5Agg
- Python version: 3.9.1
- Other libraries: Numpy 1.19.4
Matplotlib and other packages installed via the Manjaro package manager.