Question

这是我的函数，变量track是一个列表，列表的每个元素都是n x 3数组：

temp = np.array(np.zeros((n, n)))
for j in range(n-1):
    for w in range(j + 1, n):  
        mindistance = np.zeros(len(tracks[j]))
        for i in range(len(tracks[j])):   
            mindistance[i] = np.linalg.norm(min(np.fabs(np.array(tracks[w]) - tracks[j][i])))
        temp[j][w]=np.sum(mindistance)/len(tracks[j])

我正在尝试计算列表数组之间的最小距离，这些距离表示空间中的3d行，但是我收到了错误：

ValueError：具有多个元素的数组的真值是不明确的。使用a.any（）或a.all（）。

错误可能与调用min()有关，但我无法解决。以下是错误追溯：

Traceback (most recent call last):

  File "<ipython-input-14-7fb640816626>", line 1, in <module>
    runfile('/Users/G_Laza/Desktop/functions/Main.py', wdir='/Users/G_Laza/Desktop/functions')

  File "/Applications/Spyder.app/Contents/Resources/lib/python2.7/spyderlib/widgets/externalshell/sitecustomize.py", line 580, in runfile
    execfile(filename, namespace)

  File "/Users/G_Laza/Desktop/functions/Main.py", line 42, in <module>
    tempA = distance_calc.dist_calc(len(subset_A), subset_A)  # distance matrix calculation

  File "distance_calc.py", line 23, in dist_calc
    mindistance[i] = np.linalg.norm(min(np.fabs(np.array(tracks[w]) - tracks[j][i])))

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Answer 1

发生错误是因为您无法确定完整数组是True还是False。什么是数组的布尔状态，其中所有元素都是True但只有一个？

min对参数进行迭代，并将每个元素与另一个元素进行比较，每个比较结果在布尔值中。迭代1-d numpy数组会产生单个元素 - min适用于1-d numpy数组。

>>> a
array([-4, -3, -2, -1,  0,  1,  2,  3,  4])
>>> for thing in a:
     print thing,


-4 -3 -2 -1 0 1 2 3 4
>>> min(a)
-4
>>>

迭代2-d numpy数组会产生行。

>>> b
array([[-4, -3, -2],
       [-1,  0,  1],
       [ 2,  3,  4]])
>>> for thing in b:
     print thing

[-4 -3 -2]
[-1  0  1]
[2 3 4]
>>>

min因为正在比较数组和The truth value of an array with more than one element is ambiguous而无法为二维数组工作。

>>> c
array([0, 1, 2, 3])
>>> c < 2
array([ True,  True, False, False], dtype=bool)
>>> bool(c < 2)

Traceback (most recent call last):
  File "<pyshell#74>", line 1, in <module>
    bool(c < 2)
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
>>> 
>>> bool(np.array((True, True)))

Traceback (most recent call last):
  File "<pyshell#75>", line 1, in <module>
    bool(np.array((True, True)))
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
>>> 
>>> bool(np.array((True, False)))

Traceback (most recent call last):
  File "<pyshell#76>", line 1, in <module>
    bool(np.array((True, False)))
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
>>>

如果您需要找到具有最小值的元素，请使用numpy.amin或ndarray.min方法。

>>> 
>>> np.amin(b)
-4
>>> b.min()
-4
>>>

简单Python计算中的ValueError

1 个答案: