Assume the following 3D numpy array:
array([[[4, 1, 3, 5, 0, 1, 5, 4, 3],
[2, 3, 3, 2, 1, 0, 5, 5, 4],
[5, 3, 0, 2, 2, 2, 5, 3, 2],
[0, 3, 1, 0, 2, 4, 1, 1, 5],
[2, 0, 0, 1, 4, 0, 3, 5, 3]],
[[2, 2, 4, 1, 3, 4, 1, 1, 5],
[2, 2, 3, 5, 5, 4, 0, 2, 0],
[4, 0, 5, 3, 1, 3, 1, 1, 1],
[4, 5, 0, 0, 5, 3, 3, 2, 4],
[0, 3, 4, 5, 4, 5, 4, 2, 3]],
[[1, 3, 2, 2, 0, 4, 5, 0, 2],
[5, 0, 5, 2, 3, 5, 5, 3, 1],
[0, 5, 3, 2, 2, 0, 4, 2, 3],
[4, 4, 0, 3, 2, 1, 5, 3, 0],
[0, 0, 2, 4, 0, 5, 2, 0, 0]]])
Given a list [3, 4, 8]
,
is it possible to slice the given tensor without using a for loop?
For example to take the 3rdth column from [0, :, :]
, 4th column from [1, :, :]
and 8th column from [2, :, :]
to obtain:
array([[5, 2, 2, 0, 1],
[3, 5, 1, 5, 4],
[2, 1, 3, 0, 0]])
Here's one way with np.take_along_axis
-
In [73]: idx = np.array([3,4,8])
# a is input array
In [72]: np.take_along_axis(a,idx[:,None,None],axis=2)[:,:,0]
Out[72]:
array([[5, 2, 2, 0, 1],
[3, 5, 1, 5, 4],
[2, 1, 3, 0, 0]])
Another with the explicit integer-indexing -
In [79]: a[np.arange(len(idx)),:,idx]
Out[79]:
array([[5, 2, 2, 0, 1],
[3, 5, 1, 5, 4],
[2, 1, 3, 0, 0]])