Matplotlib：ValueError：x和y必须具有相同的第一个维度

Question

我正在尝试拟合最适合我的matplotlib图的线性线。我不断得到x和y没有相同的第一个维度的错误。但他们都有15个长度。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()

Answer 1

你应该制作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，它会生成预期图。如果它们是列表，m * x将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，而非标准Python float。

我实际上认为这是Numpy有点可疑的行为。在普通的Python中，将列表与整数相乘只重复列表：

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（我认为应该这样）：

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，这是非常意外的行为。最好的办法是提出一个错误（这样你就可以自己发现问题，而不必在Stackoverflow上提出你的问题），或者只显示预期的逐元素乘法（你的代码将在其中运行） 。有趣的是，列表和Numpy标量之间的添加确实有效：

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

Answer 2

将列表更改为numpy阵列将完成工作！

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

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]) # x is a numpy array now
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]) # y is a numpy array now
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()