NumPy布尔数组警告？

Question

I have a few numpy arrays, lets say a , b , and c , and have created a mask to apply to all of them.

I am trying to mask them as such:

a = a[mask]

where mask is a bool array. It is worth noting that I have verified that

len(a) = len(b) = len(c) = len(mask)

And I am getting a rather cryptic sounding warning:

FutureWarning: in the future, boolean array-likes will be handled as a boolean array index

Answer 1

False == 0, and True == 1. If your mask is a list, and not an ndarray, you can get some unexpected behaviour:

>>> a = np.array([1,2,3])
>>> mask_list = [True, False, True]
>>> a[mask_list]
__main__:1: FutureWarning: in the future, boolean array-likes will be handled as a boolean array index
array([2, 1, 2])

where this array is made up of a[1], a[0], and a[1], just like

>>> a[np.array([1,0,1])]
array([2, 1, 2])

On the other hand:

>>> mask_array = np.array(mask_list)
>>> mask_array
array([ True, False,  True], dtype=bool)
>>> a[mask_array]
array([1, 3])

The warning is telling you that eventually a[mask_list] will give you the same as a[mask_array] (which is probably what you wanted it to give you in the first place.)