NumPy 中的花式索引

Question

What is happening here?? I'm not able to get it.

a = np.arange(12).reshape(3,4)
i = np.array( [ [0,1],[1,2] ] )
j = np.array( [ [2,1],[3,3] ] )
print(a[i,j])

Output looks like this

                 [[ 2,  5],
                 [ 7, 11]]

Answer 1

Maybe this rearrangement of the indices will help

[0,1],  [2,1]
[1,2],  [3,3] 

or

(0,2)  (1,1)
(1,3)  (2,3)

It's picking 4 values, using the 4 indices from each of the 2 arrays.

a[0,2], a[1,1] etc