Stack 1-D arrays as columns into a 2-D array.
Take a sequence of 1-D arrays and stack them as columns
to make a single 2-D array. 2-D arrays are stacked as-is,
just like with hstack. 1-D arrays are turned into 2-D columns
Arrays to stack. All of them must have the same first dimension.
The array formed by stacking the given arrays.
>>> a = np.array((1,2,3))
>>> b = np.array((2,3,4))