Arrays can be combined in various ways. This process in NumPy is referred to as stacking. Stacking can take various forms, including horizontal, vertical, and depth-wise stacking. To demonstrate this, we will use the following two arrays (a and b):

In [59]:
   # creating two arrays for examples
   a = np.arange(9).reshape(3, 3)
   b = (a + 1) * 10
   a

Out[59]:
   array([[0, 1, 2],
          [3, 4, 5],
          [6, 7, 8]])

In [60]:
   b

Out[60]:
   array([[10, 20, 30],
          [40, 50, 60],
          [70, 80, 90]])

Horizontal stacking combines two arrays in a manner where the columns of the second array are placed to the right of those in the first array. The function actually stacks the two items provided in a two-element tuple. The result is a new array with data copied from the two that are specified:

In [61]:
   # horizontally stack the two arrays
   # b becomes columns of a to the right of a's columns
   np.hstack((a, b))

Out[61]:
   array([[ 0,  1,  2, 10, 20...