Python: "Use a.any() or a.all()" 遍历 numpy.ndarray

Question

像这样的numpy.ndarray：

myarray=
array([[ 0.47174344,  0.45314669,  0.46395022,  0.47440382,  0.50709627,
         0.53350065,  0.5233444 ,  0.49974663,  0.48721607,  0.46239652,
         0.4693633 ,  0.47263569,  0.47591957,  0.436558  ,  0.43335574,
         0.44053621,  0.42814804,  0.43201894,  0.43973886,  0.44125302,
         0.41176999],
       [ 0.46509004,  0.46221505,  0.48824086,  0.50088744,  0.53040384,
         0.53592231,  0.49710228,  0.49821022,  0.47720381,  0.49096272,
         0.50438366,  0.47173162,  0.48813669,  0.45032002,  0.44776794,
         0.43910269,  0.43326132,  0.42064458,  0.43472954,  0.45577299,
         0.43604956]])

我想计算有多少单元格超过给定值，比方说 0.5，然后将那些不超过给定值的单元格设置为 0.0。这就是我所做的：

count=0 
value=0.5
for i in range(myarray.shape[0]):
   for j in range(myarray.shape[1]):
       if myarray[i][j]<value:
          myarray[i][j]=0 
       elif myarray[i][j]>=value:     
          count=count+1 
percentage=round(100*count/(myarray.shape[0]*myarray.shape[1]),2)

但是，我收到此错误：ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()，指向我检查 if myarray[i][j]<value 的行。

为什么会出现这种情况，如何解决？真值是多少？

Answer 1

通常情况下，您可以比较两个数字以获得真值。例如：

elem = 5
if elem < 6:
    # do something

相当于：

if true:
    # do something

但是，您不能将数组与值进行比较。例如：

elem = [5,7]
if elem < 6:
    # this doesn't make sense

相反，您可以获得任何或所有元素是否满足条件的真值。例如：

elem = np.array([5,7])
if np.any(elem<6):
    # this is true, because 5 < 6
if np.all(elem<6):
    # this isn't true, because 7 > 6

我运行你上面的示例代码并没有发现错误，所以我不确定问题是什么。但这是你应该注意的。考虑打印您正在比较的元素以查看它是否是一个数组。

此外，这是执行您想要执行的操作的较短方法：

myarray = np.array( putarrayhere )
count = sum(myarray >= value)

Answer 2

是的，我认为您的 numpy.array 有一个额外的括号或者它包含另一个数组。

尝试手动将数组设置为

myarray=np.array([[ 0.47174344,  0.45314669,  0.46395022,  0.47440382,  0.50709627,0.53350065,  0.5233444 ,  0.49974663,  0.48721607,  0.46239652, 0.4693633 ,  0.47263569,  0.47591957,  0.436558  ,  0.43335574,0.44053621,  0.42814804,  0.43201894,  0.43973886, 0.44125302, 0.41176999],[ 0.46509004,  0.46221505,  0.48824086,  0.50088744,  0.53040384,0.53592231,  0.49710228,  0.49821022,  0.47720381,  0.49096272,0.50438366,  0.47173162,  0.48813669,  0.45032002,  0.44776794,0.43910269,  0.43326132,  0.42064458,  0.43472954,  0.45577299,0.43604956]])

代码有效

但设置：

myarray=np.array([[[ 0.47174344,  0.45314669,  0.46395022,  0.47440382,  0.50709627,0.53350065,  0.5233444 ,  0.49974663,  0.48721607,  0.46239652, 0.4693633 ,  0.47263569,  0.47591957,  0.436558  ,  0.43335574,0.44053621,  0.42814804,  0.43201894,  0.43973886, 0.44125302, 0.41176999],[ 0.46509004,  0.46221505,  0.48824086,  0.50088744,  0.53040384,0.53592231,  0.49710228,  0.49821022,  0.47720381,  0.49096272,0.50438366,  0.47173162,  0.48813669,  0.45032002,  0.44776794,0.43910269,  0.43326132,  0.42064458,  0.43472954,  0.45577299,0.43604956]]])

产生了类似的错误

Answer 3

不管错误你可以简单地做：

myarray[myarray<value]=0
np.count_nonzero(myarray)

得到你想要的结果

Python: "Use a.any() or a.all()" 遍历 numpy.ndarray

Python: "Use a.any() or a.all()" while traversing a numpy.ndarray

python

numpy

for-loop

ambiguity