python - Matplotlib:TypeError:不能将序列乘以 'numpy.float64' 类型的非整数

Question

我正在尝试将一条最适合我的 matplotlib 图表的线性线拟合。我不断收到 x 和 y 第一维不同的错误。但是它们的长度都是 15。我做错了什么？

import matplotlib.pyplot as plt
from scipy import stats
import numpy as np

x = [0.46,0.59,0.68,0.99,0.39,0.31,1.09,0.77,0.72,0.49,0.55,0.62,0.58,0.88,0.78]
y = [0.315,0.383,0.452,0.650,0.279,0.215,0.727,0.512,0.478,0.335,0.365,0.424,0.390,0.585,0.511]
xerr = [0.01]*15
yerr = [0.001]*15

plt.rc('font', family='serif', size=13)
m, b = np.polyfit(x, y, 1)
plt.plot(x,y,'s',color='#0066FF')
plt.plot(x, m*x + b, 'r-') #BREAKS ON THIS LINE
plt.errorbar(x,y,xerr=xerr,yerr=0,linestyle="None",color='black')
plt.xlabel('$\Delta t$ $(s)$',fontsize=20)
plt.ylabel('$\Delta p$ $(hPa)$',fontsize=20)
plt.autoscale(enable=True, axis=u'both', tight=False)
plt.grid(False)
plt.xlim(0.2,1.2)
plt.ylim(0,0.8)
plt.show()

错误

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_34116/1820029981.py in <module>
      7 m, b = np.polyfit(x, y, 1)
      8 plt.plot(x,y,'s',color='#0066FF')
----> 9 plt.plot(x, m*x + b, 'r-') #BREAKS ON THIS LINE
     10 plt.errorbar(x,y,xerr=xerr,yerr=0,linestyle="None",color='black')
     11 plt.xlabel('$\Delta t$ $(s)$',fontsize=20)

TypeError: can't multiply sequence by non-int of type 'numpy.float64'

Answer 1

您应该制作 x 和 y numpy 数组，而不是列表:

x = np.array([0.46,0.59,0.68,0.99,0.39,0.31,1.09,
              0.77,0.72,0.49,0.55,0.62,0.58,0.88,0.78])
y = np.array([0.315,0.383,0.452,0.650,0.279,0.215,0.727,0.512,
              0.478,0.335,0.365,0.424,0.390,0.585,0.511])

通过此更改，它会产生预期的情节。如果它们是列表，则 m * x 不会产生您期望的结果，而是一个空列表。请注意，m 是 numpy.float64 标量，而不是标准 Python float。

我实际上认为 Numpy 的这种行为有点可疑。在普通 Python 中，将列表与整数相乘只会重复列表:

In [42]: 2 * [1, 2, 3]
Out[42]: [1, 2, 3, 1, 2, 3]

将列表与 float 相乘会产生错误(我认为应该如此):

In [43]: 1.5 * [1, 2, 3]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-43-d710bb467cdd> in <module>()
----> 1 1.5 * [1, 2, 3]
TypeError: can't multiply sequence by non-int of type 'float'

奇怪的是，将 Python 列表与 Numpy 标量相乘显然有效:

In [45]: np.float64(0.5) * [1, 2, 3]
Out[45]: []

In [46]: np.float64(1.5) * [1, 2, 3]
Out[46]: [1, 2, 3]

In [47]: np.float64(2.5) * [1, 2, 3]
Out[47]: [1, 2, 3, 1, 2, 3]

所以看起来 float 被截断为 int，之后你会得到重复列表的标准 Python 行为，这是非常出乎意料的行为。最好的办法是提出一个错误(这样您就可以自己发现问题，而不必在 Stackoverflow 上提问)或只显示预期的元素乘法(您的代码在其中可以正常工作) .有趣的是，列表和 Numpy 标量之间的加法确实有效:

In [69]: np.float64(0.123) + [1, 2, 3]
Out[69]: array([ 1.123,  2.123,  3.123])