可以给出不不止一维的索引

我们也可以给出不不止一维的索引，每一维的索引数组必须有相同的形状。

>>> a = arange(12).reshape(3,4)
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])
>>> i = array( [ [0,1],                        # indices for the first dim of a
...              [1,2] ] )
>>> j = array( [ [2,1],                        # indices for the second dim
...              [3,3] ] )
>>>
>>> a[i,j]                                     # i and j must have equal shape
array([[ 2,  5],
       [ 7, 11]])
>>>
>>> a[i,2]
array([[ 2,  6],
       [ 6, 10]])
>>>
>>> a[:,j]                                     # i.e., a[ : , j]
array([[[ 2,  1],
        [ 3,  3]],
       [[ 6,  5],
        [ 7,  7]],
       [[10,  9],
        [11, 11]]])

自然，我们可以把i和j放到序列中(比如说列表)然后通过list索引。

>>> l = [i,j]
>>> a[l]                                       # equivalent to a[i,j]
array([[ 2,  5],
       [ 7, 11]])

然而，我们不能把i和j放在一个数组中，因为这个数组将被解释成索引a的第一维。

>>> s = array( [i,j] )
>>> a[s]                                       # not what we want
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
 in ()
----> 1 a[s]

IndexError: index (3) out of range (0<=index<2) in dimension 0
>>>
>>> a[tuple(s)]                                # same as a[i,j]
array([[ 2,  5],
       [ 7, 11]])

>>> a = arange(12).reshape(3,4)
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])
>>> i = array( [ [0,1],                        # indices for the first dim of a
... [1,2] ] )
>>> a[i]
array([[[ 0,  1,  2,  3],
        [ 4,  5,  6,  7]],

       [[ 4,  5,  6,  7],
        [ 8,  9, 10, 11]]])
>>> i.shape
(2, 2)
>>> a[i].shape
(2, 2, 4)
>>> a.shape
(3, 4)
>>> j = array( [ [2,1],                        # indices for the second dim
... [3,3] ] )
>>> a[i,j]
array([[ 2,  5],
       [ 7, 11]])
>>> a[i,2]
array([[ 2,  6],
       [ 6, 10]])
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])
>>> i
array([[0, 1],
       [1, 2]])
>>> j
array([[2, 1],
       [3, 3]])
>>> a[:,j]
array([[[ 2,  1],
        [ 3,  3]],

       [[ 6,  5],
        [ 7,  7]],

       [[10,  9],
        [11, 11]]])
>>> l = [i,j]
>>> l
[array([[0, 1],
       [1, 2]]), array([[2, 1],
       [3, 3]])]
>>> a[l]
array([[ 2,  5],
       [ 7, 11]])
>>>