numpy.vstack() in python

Last Updated : 25 Apr, 2025

numpy.vstack() is a function in NumPy used to stack arrays vertically (row-wise). It takes a sequence of arrays as input and returns a single array by stacking them along the vertical axis (axis 0).

Example: Vertical Stacking of 1D Arrays Using numpy.vstack()

Python

import numpy as geek

a = geek.array([ 1, 2, 3] )
print ("1st Input array : \n", a) 

b = geek.array([ 4, 5, 6] )
print ("2nd Input array : \n", b) 

res = geek.vstack((a, b))
print ("Output vertically stacked array:\n ", res)

Output

1st Input array : 
 [1 2 3]
2nd Input array : 
 [4 5 6]
Output vertically stacked array:
  [[1 2 3]
 [4 5 6]]

Explanation: The two 1D arrays a and b are stacked vertically using np.vstack(), combining them into a 2D array where each input array forms a row.

Syntax

numpy.vstack(tup)

Parameters:

tup: [sequence of ndarrays] Tuple containing arrays to be stacked. The arrays must have the same shape along all but the first axis.

Return: [stacked ndarray] The stacked array of the input arrays.

Vertical Stacking of 2D Arrays Using numpy.vstack()

This code shows how to vertically stack two 2D arrays using numpy.vstack(), resulting in a combined 2D array.

Python

import numpy as geek

a = geek.array([[ 1, 2, 3], [ -1, -2, -3]] )
print ("1st Input array : \n", a) 

b = geek.array([[ 4, 5, 6], [ -4, -5, -6]] )
print ("2nd Input array : \n", b) 

res = geek.vstack((a, b))
print ("Output stacked array :\n ", res)

Output

1st Input array : 
 [[ 1  2  3]
 [-1 -2 -3]]
2nd Input array : 
 [[ 4  5  6]
 [-4 -5 -6]]
Output stacked array :
  [[ 1  2  3]
 [-1 -2 -3]
 [ 4  5  6]
 [-4 -5 -6]]

Explanation: Two 2D arrays a and b are vertically stacked, creating a new 2D array where each original array becomes a set of rows in the resulting array.