MatPlotLib,datetimes和TypeError:输入类型不支持ufunc'isfinite'...

Question

这是一小段代码,它在图形的两行之间产生一个填充区域:

import matplotlib.pyplot as plt
import numpy as np

x = np.arange(0.0, 2, 0.01)
y1 = np.sin(2 * np.pi * x)
y2 = 1.2 * np.sin(4 * np.pi * x)

fig, ax1 = plt.subplots(1, 1, sharex=True)

# Test support for masked arrays.
ax1.fill_between(x, 0, y1)
ax1.set_ylabel('between y1 and 0')
y2 = np.ma.masked_greater(y2, 1.0)
ax1.plot(x, y1, x, y2, color='black')
ax1.fill_between(
    x, y1, y2, where=y2 >= y1,
    facecolor='green',
    interpolate=True)
ax1.fill_between(x, y1, y2, where=y2 <= y1, facecolor='red', interpolate=True)
ax1.set_title('Now regions with y2>1 are masked')

# Show the plot.
plt.show()

它看起来像这样:

现在,更改开始,以便x现在是日期时间对象的集合,如下所示:

import datetime

x1 = np.arange(0.0, 2, 0.01)
now = np.datetime64(datetime.datetime.now())
x = np.array([now - np.timedelta64(datetime.timedelta(seconds=i)) for i in range(200)])
y1 = np.sin(2 * np.pi * x1)
y2 = 1.2 * np.sin(4 * np.pi * x1)

收益率:

Traceback (most recent call last):                                                File "fill_between_demo.py", line 21, in <module>                             
    ax1.fill_between(x, 0, y1)                                                  
  File "/home/usr/.virtualenvs/raiju/lib/python3.6/site-packages/matplotlib/__init__.py", line 1898, in inner                                                  
    return func(ax, *args, **kwargs)                                            
  File "/home/usr/.virtualenvs/raiju/lib/python3.6/site-packages/matplotlib/axes/_axes.py", line 4778, in fill_between                                         
    x = ma.masked_invalid(self.convert_xunits(x))                               
  File "/home/usr/.virtualenvs/raiju/lib/python3.6/site-packages/numpy/ma/core.py", line 2388, in masked_invalid                                               
    condition = ~(np.isfinite(a))                                               
TypeError: ufunc 'isfinite' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''     

为什么会发生这种情况以及如何解决？

请注意,绘制数据(也就是不使用fill*)可以正常工作.

Answer 1

问题是,isfinite没有为numpy.datetime64dtype 定义numpy ufunc.但是,我们正努力改变这种状况.numpy的github上的这个问题正在这个pull-request中进行,但是只要没有完成并合并,你将无法isfinite在该dtype 上使用.matplotlib.pyplot.fill_between当调用numpy.ma.masked_invalid掩码输入数组的所有无效条目时,这是一个隐式使用此函数的问题.

虽然有一个解决方法.正如在关于绘制类型的大熊猫的类似问题的答案中所指出的,pandas为(以及其他)具有matplotlib 的dtype numpy数组注册了一个自定义转换器.要使用它,您只需导入pandas:fill_betweenSeriesdatetime64datetime64

import numpy as np
import matplotlib.pyplot as plt
import datetime
# import pandas for its converter that is then used in pyplot!
import pandas

x1 = np.arange(0.0, 2, 0.01)
now = np.datetime64(datetime.datetime.now())
x = np.array([now - np.timedelta64(datetime.timedelta(seconds=i))
              for i in range(200)])
y1 = np.sin(2 * np.pi * x1)
y2 = 1.2 * np.sin(4 * np.pi * x1)

fig, ax1 = plt.subplots(1, 1, sharex=True)

# Test support for masked arrays.
ax1.fill_between(x, 0, y1)
ax1.set_ylabel('between y1 and 0')
y2 = np.ma.masked_greater(y2, 1.0)
ax1.plot(x, y1, x, y2, color='black')
ax1.fill_between(
    x, y1, y2, where=y2 >= y1,
    facecolor='green',
    interpolate=True)
ax1.fill_between(x, y1, y2, where=y2 <= y1, facecolor='red', interpolate=True)
ax1.set_title('Now regions with y2>1 are masked')

# Show the plot.
plt.show()

将工作,并为您提供所需的输出: