Numpy array of multiple indices replace with a different matrix

Question

I have an array of 2d indices.

indices = [[2,4], [6,77], [102,554]]

Now, I have a different 4-dimensional array, arr, and I want to only extrac

Answer 1

We need to index into the first two axes with the two columns from indices (thinking of it as an array).

Thus, simply convert to array and index, like so -

indices_arr = np.array(indices)
out = arr[indices_arr[:,0], indices_arr[:,1]]

Or we could extract those directly without converting to array and then index -

d0,d1 = [i[0] for i in indices], [i[1] for i in indices]
out = arr[d0,d1]

Another way to extract the elements would be with conversion to tuple, like so -

out = arr[tuple(indices_arr.T)]

If indices is already an array, skip the conversion process and use indices in places where we had indices_arr.

Answer 2

Try using the take function of numpy arrays. Your code should be something like:

outputarray= np.take(arr,indices)