返回Python中未被索引数组引用的元素

Question

假设我在Python中有一个数组,例如:

my_array = np.array([10, -5, 4, ...])
my_indices = np.array([0, 3, 10, ...])

我怎样才能有效地获得:

1. 列表索引的my_array不在my_indices
2. 列表元素中my_array不提及的my_indices(琐碎1,但也许有一个直接的方式)

Answer 1

我可能会这样做:

>>> import numpy as np
>>> a = np.random.random(10)  # set up a random array to play with
>>> a
array([ 0.20291643,  0.89973074,  0.14291639,  0.53535553,  0.21801353,
        0.05582776,  0.64301145,  0.56081956,  0.85771335,  0.6032354 ])
>>>
>>> b = np.array([0,5,6,9])  # indices we *don't want*
>>> mask = np.ones(a.shape,dtype=bool)
>>> mask[b] = False          # Converted to a mask array of indices we *do want*
>>> mask
array([False,  True,  True,  True,  True, False, False,  True,  True, False], dtype=bool)
>>>
>>> np.arange(a.shape[0])[mask]  #This gets you the indices that aren't in your original
array([1, 2, 3, 4, 7, 8])
>>> a[mask]  #This gets you the elements not in your original.
array([ 0.89973074,  0.14291639,  0.53535553,  0.21801353,  0.56081956,
        0.85771335])