using an numpy array as indices of the 2nd dim of another array? [duplicate]

Answer 1

C = np.array([A[i][j] for i,j in enumerate(B)])

Answer 2

You can use NumPy's purely integer array indexing -

A[np.arange(A.shape[0]),B.ravel()]

Sample run -

In [57]: A
Out[57]: 
array([[0, 1],
       [2, 3],
       [4, 5]])

In [58]: B
Out[58]: 
array([[1],
       [0],
       [1]])

In [59]: A[np.arange(A.shape[0]),B.ravel()]
Out[59]: array([1, 2, 5])

Please note that if B is a 1D array or a list of such column indices, you could simply skip the flattening operation with .ravel().

Sample run -

In [186]: A
Out[186]: 
array([[0, 1],
       [2, 3],
       [4, 5]])

In [187]: B
Out[187]: [1, 0, 1]

In [188]: A[np.arange(A.shape[0]),B]
Out[188]: array([1, 2, 5])