I feel silly, because this is such a simple thing, but I haven't found the answer either here or anywhere else.
Is there no straightforward way of indexing a numpy array with another?
Say I have a 2D array
>> A = np.asarray([[1, 2], [3, 4], [5, 6], [7, 8]])
array([[1, 2],
[3, 4],
[5, 6],
[7, 8]])
if I want to access element [3,1] I type
>> A[3,1]
8
Now, say I store this index in an array
>> ind = np.array([3,1])
and try using the index this time:
>> A[ind]
array([[7, 8],
[3, 4]])
the result is not A[3,1]
The question is: having arrays A and ind, what is the simplest way to obtain A[3,1]?
Just use a tuple:
>>> A[(3, 1)]
8
>>> A[tuple(ind)]
8
The A[]
actually calls the special method __getitem__
:
>>> A.__getitem__((3, 1))
8
and using a comma creates a tuple:
>>> 3, 1
(3, 1)
Putting these two basic Python principles together solves your problem.
You can store your index in a tuple in the first place, if you don't need NumPy array features for it.
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