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pcolormesh throws UFuncTypeError if np.datetime64() and shading='nearest #19191

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Yoshi2112 opened this issue Dec 29, 2020 · 1 comment
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pcolormesh throws UFuncTypeError if np.datetime64() and shading='nearest #19191

Yoshi2112 opened this issue Dec 29, 2020 · 1 comment
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@Yoshi2112
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Yoshi2112 commented Dec 29, 2020 •
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Bug report

Bug summary

For people who use numpy.datetime64() arrays with pcolormesh, a DeprecationWarning has been appearing prompting users to specify a shading kwarg 'nearest', 'auto' or 'gouraud' since shading='flat' is being deprecated. However, passing 'nearest' results in a UFuncTypeError when using 'nearest' due to a casting issue in _axes.py from _interp_grid()

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt

times = np.arange(np.datetime64('2020-12-01'), np.datetime64('2020-12-31'))
yaxis = np.arange(0, 20)
caxis = np.random.normal(0.0, 1.0, (times.shape[0], yaxis.shape[0]))

plt.pcolormesh(times, yaxis, caxis.T, shading='nearest')
plt.show()

Actual outcome

Traceback (most recent call last):

  File "..\test.py", line 15, in <module>
    plt.pcolormesh(times, yaxis, caxis.T, shading='nearest')

  File "C:\Users\iarey\anaconda3\lib\site-packages\matplotlib\pyplot.py", line 2801, in pcolormesh
    __ret = gca().pcolormesh(

  File "C:\Users\iarey\anaconda3\lib\site-packages\matplotlib\__init__.py", line 1438, in inner
    return func(ax, *map(sanitize_sequence, args), **kwargs)

  File "C:\Users\iarey\anaconda3\lib\site-packages\matplotlib\axes\_axes.py", line 6093, in pcolormesh
    X, Y, C, shading = self._pcolorargs('pcolormesh', *args,

  File "C:\Users\iarey\anaconda3\lib\site-packages\matplotlib\axes\_axes.py", line 5651, in _pcolorargs
    X = _interp_grid(X)

  File "C:\Users\iarey\anaconda3\lib\site-packages\matplotlib\axes\_axes.py", line 5633, in _interp_grid
    if not (np.all(dX >= 0) or np.all(dX <= 0)):

UFuncTypeError: Cannot cast ufunc 'greater_equal' input 0 from dtype('<m8[D]') to dtype('<m8') with casting rule 'same_kind'

Expected outcome
A pcolormesh timeseries plot with random data and a np.datetime64() x-axis.

Matplotlib version

  • Operating system: Windows 10
  • Matplotlib version: 3.3.2 via standard conda
  • Matplotlib backend: Qt5Agg
  • Python version: 3.8.5
  • Jupyter version (if applicable):
  • Other libraries: numpy-1.19.2
@jklymak
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jklymak commented Dec 29, 2020

This is a duplicate of #18547, and closed by #18549 released with 3.3.3

In the case of getting the old behaviour you can just drop the last element (like flat does) if you can't upgrade for some reason (caxis[:-1, :-1].T), or ignore the deprecation.

@jklymak jklymak closed this as completed Dec 29, 2020
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