Time for action – stacking arrays

First, let's set up some arrays:

In: a = arange(9).reshape(3,3)
In: a
Out:
array([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])
In: b = 2 * a
In: b
Out:
array([[ 0,  2,  4],
       [ 6,  8, 10],
       [12, 14, 16]])

1. Horizontal stacking: Starting with horizontal stacking, we will form a tuple of ndarrays and give it to the hstack function. This is shown as follows:

   In: hstack((a, b))
   Out:
   array([[ 0,  1,  2,  0,  2,  4],
          [ 3,  4,  5,  6,  8, 10],
          [ 6,  7,  8, 12, 14, 16]])

   We can achieve the same with the concatenate function, which is shown as follows:

   In: concatenate((a, b), axis=1)
   Out:
   array([[ 0,  1,  2,  0,  2,  4],
          [ 3,  4,  5,  6,  8, 10],
          [ 6,  7,  8, 12, 14, 16]])

   

2. Vertical stacking: With vertical stacking, again, a tuple is formed. This time, it is given to the vstack function. This can be seen as follows:

   In: vstack((a, b))
   Out:
   array([[ 0,  1,  2],
          [ 3,  4,  5],
          [ 6,  7,  8],
          [ 0,  2,  4],
         ...