使用matplotlib axes.fill_between()时浮点数组触发isfinite类型错误

问题描述 #

尝试用以下代码填充x轴与函数曲线之间的区域时触发TypeError：

import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np

s1_norm_x = np.array([0, l-b, l-b, l])
s1_norm_y = np.array([G_x, G_x, 0, 0])

figure, axs = plt.subplots(3, 1, sharex=True)
ax_norm, ax_quer, ax_bieg = axs
ax_norm.set_xticks([0, l-b, l])

ax_norm.set_xlabel('x')
ax_norm.set_ylabel("Normalkraft - N(x) [kN]")
ax_norm.plot(s1_norm_x, s1_norm_y, color='blue')
ax_norm.fill_between(s1_norm_x, s1_norm_y, facecolor = 'red', alpha = 0.3)

plt.show()

变量取值：l=1.1, b=0.8, G_x=-3.2031250000

改用长度为4的整数数组替换s1_norm_x和s1_norm_y时，填充显示正常但无法与曲线对齐。

完整错误信息：

TypeError                                 Traceback (most recent call last)
Cell In[24], line 11
      9 ax_norm.set_ylabel("Normalkraft - N(x) [kN]")
     10 ax_norm.plot(s1_norm_x, s1_norm_y, color='blue')
---> 11 ax_norm.fill_between(s1_norm_x, s1_norm_y, facecolor = 'red', alpha = 0.3)
     13 plt.show()

File ~\anaconda3\lib\site-packages\matplotlib\__init__.py:1442, in _preprocess_data.<locals>.inner(ax, data, *args, **kwargs)
   1439 @functools.wraps(func)
   1440 def inner(ax, *args, data=None, **kwargs):
   1441     if data is None:
-> 1442         return func(ax, *map(sanitize_sequence, args), **kwargs)
   1444     bound = new_sig.bind(ax, *args, **kwargs)
   1445     auto_label = (bound.arguments.get(label_namer)
   1446                   or bound.kwargs.get(label_namer))

File ~\anaconda3\lib\site-packages\matplotlib\axes\_axes.py:5431, in Axes.fill_between(self, x, y1, y2, where, interpolate, step, **kwargs)
   5429 def fill_between(self, x, y1, y2=0, where=None, interpolate=False,
   5430                  step=None, **kwargs):
-> 5431     return self._fill_between_x_or_y(
   5432         "x", x, y1, y2,
   5433         where=where, interpolate=interpolate, step=step, **kwargs)

File ~\anaconda3\lib\site-packages\matplotlib\axes\_axes.py:5336, in Axes._fill_between_x_or_y(self, ind_dir, ind, dep1, dep2, where, interpolate, step, **kwargs)
   5332         kwargs["facecolor"] = \
   5333             self._get_patches_for_fill.get_next_color()
   5335 # Handle united data, such as dates
-> 5336 ind, dep1, dep2 = map(
   5337     ma.masked_invalid, self._process_unit_info(
   5338         [(ind_dir, ind), (dep_dir, dep1), (dep_dir, dep2)], kwargs))
   5340 for name, array in [
   5341         (ind_dir, ind), (f"{dep_dir}1", dep1), (f"{dep_dir}2", dep2)]:
   5342     if array.ndim > 1:

File ~\anaconda3\lib\site-packages\numpy\ma\core.py:2366, in masked_invalid(a, copy)
   2364     cls = type(a)
   2365 else:
-> 2366     condition = ~(np.isfinite(a))
   2367     cls = MaskedArray
   2368 result = a.view(cls)

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''

解决方法 #

错误核心是数组中存在非数值类型元素，或变量l、b、G_x未被正确定义为数值类型。

修复步骤 #

• 明确变量类型：在创建数组前，将l、b、G_x定义为浮点数：

  l = 1.1
  b = 0.8
  G_x = -3.2031250000
  

• 强制数组数值类型：创建数组时指定dtype=np.float64，确保所有元素为数值：

  s1_norm_x = np.array([0, l-b, l-b, l], dtype=np.float64)
  s1_norm_y = np.array([G_x, G_x, 0, 0], dtype=np.float64)
  

• 验证数组内容：打印数组确认元素类型：

  print(s1_norm_x)
  print(s1_norm_y)
  

完整修复代码 #

import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np

# 定义数值变量
l = 1.1
b = 0.8
G_x = -3.2031250000

# 创建数值类型数组
s1_norm_x = np.array([0, l-b, l-b, l], dtype=np.float64)
s1_norm_y = np.array([G_x, G_x, 0, 0], dtype=np.float64)

figure, axs = plt.subplots(3, 1, sharex=True)
ax_norm, ax_quer, ax_bieg = axs
ax_norm.set_xticks([0, l-b, l])

ax_norm.set_xlabel('x')
ax_norm.set_ylabel("Normalkraft - N(x) [kN]")
ax_norm.plot(s1_norm_x, s1_norm_y, color='blue')
ax_norm.fill_between(s1_norm_x, s1_norm_y, facecolor='red', alpha=0.3)

plt.show()

修改后，fill_between可正确识别数组数值，填充区域将与曲线完美对齐，且不会触发类型错误。

内容的提问来源于stack exchange，提问作者danbuza