Python：嘗試在圖形上繪制誤差線會顯示“ ValueError：錯誤必須為[標量| N，Nx1或2xN類數組]”

Question

當我嘗試在圖形上繪制誤差線時出現以下問題。

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

col1 = []
col2 = []
col3 = []

while True:
    try:

        N = input('Please enter the full name of your numbers text file with 
its file format (e.g "Numbers.txt"): ')
        with open(N, 'r') as f:
            for line in f:
                first, second, third = line.split()
                col1.append(first)
                col2.append(second)
                col3.append(third)


    except IOError:
        sys.exit('Error: Data file is invalid! Please ensure your file 
exists. ')    
    except ValueError:
        sys.exit('Error: Data file is invalid! Please ensure your file 
contains just numbers, as well as enough of them with none missing. ')       

    else:
        break
x = np.array(col1)
y = np.array(col2)
e = np.array(col3)

N = 1
p = 0

while N <= len(col1):
    p = p + 1/(float(col3[N-1]))**2
    N = N+1


N = 1
q = 0

while N <= len(col1):
    q = q + float(col1[N-1])/(float(col3[N-1]))**2
    N = N+1


N = 1
r = 0

while N <= len(col1):
    r = r + float(col2[N-1])/(float(col3[N-1]))**2
    N = N+1


N = 1
s = 0

while N <= len(col1):
    s = s + (float(col1[N-1]))**2/(float(col3[N-1]))**2
    N=N+1


N = 1
t = 0

while N <= len(col1):   
    t = t + (float(col1[N-1])*float(col2[N-1]))/(float(col3[N-1]))**2
    N = N+1


delta = (p*s)-(q**2)


a = ((r*s)-(q*t))/delta
b = ((p*t)-(q*r))/delta
print('a is equal to: ' + str(a))
print('b is equal to: ' + str(b))


sigma_a = float(s/delta)**0.5
sigma_b = float(p/delta)**0.5
print('Error in a (Sigma_a) is equal to: ' + str(sigma_a))
print('Error in b (Sigma_b) is equal to: ' + str(sigma_b))

best_y = []
best_x = col1
N = 0
while N <= len(col1)-1:
    Y = a + ((b)*(float(col1[N])))
    best_y.append(Y)
    N = N + 1
    Y = 0



plt.plot(x, y, 'ro', best_x, best_y)
plt.errorbar(x, y, yerr=e, fmt='-o')
plt.title('Graph to show relationship between given values of x and y')
plt.xlabel('x')
plt.ylabel('y')
plt.grid(True)
plt.show()

python提供的輸出是這樣的：

"ValueError: err must be [ scalar | N, Nx1 or 2xN array-like ]"

似乎是什么問題？

順便說一句，用於提供數字的文件是txt文件，它是：

-2      2.1     -0.365635756
0       2.4      0.347433737
2       2.5      0.263774619
4       3.5     -0.244930974
6       4.2     -0.004564913

為這篇文章中的大量代碼表示歉意，但我覺得我應該包括任何可能隱藏問題的內容（對於python來說還是很新的）。

非常感謝，

盧克。

Answer 1

您沒有將文件中的字符串值轉換為浮點數。 這就是為什么matplotlib錯誤的原因。 當您通過np.array()將col1 ， col2和col3轉換為數組時，它不會將字符串值轉換為浮點數，它只會創建字符串數組（您可以通過檢查x ， y或e來看到這一點：

In[1]: x
Out[1]: 
array(['-2', '0', '2', '4', '6'], 
      dtype='<U2')

dtype='<U2'表示元素是unicode字符串。

修復代碼的最快方法是在讀取值時將值顯式轉換為float，將其添加到列列表中，如下所示：

while True:
    try:

        N = input('Please enter the full name of your numbers text file with 
its file format (e.g "Numbers.txt"): ')
        with open(N, 'r') as f:
            for line in f:
                first, second, third = line.split()
                col1.append(float(first))
                col2.append(float(second))
                col3.append(float(third))

更好的解決方法是使用Python標准庫csv模塊來處理數據文件的讀取和解析。