What is the function of np.vstack in Python?

The np.vstack function in NumPy is used to stack arrays along the vertical direction (row-wise). Specifically, np.vstack stacks two or more arrays vertically to create a new array.

For example, if there are two 2D arrays, array1 and array2, with the same number of columns, we can use np.vstack([array1, array2]) to stack them together row-wise and create a new 2D array.

import numpy as np

array1 = np.array([[1, 2, 3],
                   [4, 5, 6]])

array2 = np.array([[7, 8, 9],
                   [10, 11, 12]])

result = np.vstack([array1, array2])
print(result)

The code above will print the following results:

[[ 1  2  3]
 [ 4  5  6]
 [ 7  8  9]
 [10 11 12]]

In this way, np.vstack can assist us in stacking arrays along the vertical direction while processing arrays.