Q:

numpy.hstack() description

In the documentation, this function is said to 

Stack arrays in sequence horizontally (column wise). 

I don't really understand what "column wise" means exactly.  Can someone explain it with the example code as provided by the documentation? 
>>> a = np.array([[1],[2],[3]])
>>> b = np.array([[2],[3],[4]])
>>> np.hstack((a,b))
array([[1, 2],
       [2, 3],
       [3, 4]])

A:

Array A looks like this:
1
2
3

Array B looks like this:
2
3
4

Put array B alongside array A:
A B
1 2
2 3
3 4

This is your new array!