Index a numpy array with another array

Question

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

Answer 1

That is because by giving an array you actually ask

A[[3,1]] 

Which gives the third and first index of the 2d array instead of the first index of the third index of the array as you want.

You can use

 A[ind[0],ind[1]]

You can also use (if you want more indexes at the same time);

A[indx,indy]

Where indx and indy are numpy arrays of indexes for the first and second dimension accordingly.

See here for all possible indexing methods for numpy arrays: http://docs.scipy.org/doc/numpy-1.10.1/user/basics.indexing.html

Answer 2

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.