Python | Ways to add row/columns in numpy array
Given numpy array, the task is to add rows/columns basis on requirements to numpy array. Let’s see a few examples of this problem.
Method #1: Using np.hstack() method
# Python code to demonstrate# adding columns in numpy arrayimport numpy as npini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])# printing initial arrayprint("initial_array : ", str(ini_array));# Array to be added as columncolumn_to_be_added = np.array([1, 2, 3])# Adding column to numpy arrayresult = np.hstack((ini_array, np.atleast_2d(column_to_be_added).T))# printing resultprint ("resultant array", str(result)) |
Output:
initial_array : [[ 1 2 3] [45 4 7] [ 9 6 10]] resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method #2: Using column_stack() method
# python code to demonstrate# adding columns in numpy arrayimport numpy as npini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])# printing initial arrayprint("initial_array : ", str(ini_array));# Array to be added as columncolumn_to_be_added = np.array([1, 2, 3])# Adding column to numpy arrayresult = np.column_stack((ini_array, column_to_be_added))# printing resultprint ("resultant array", str(result)) |
Output:
initial_array : [[ 1 2 3] [45 4 7] [ 9 6 10]] resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method #3: Using np.vstack() method
- Python3
# python code to demonstrate# adding rows in numpy arrayimport numpy as npini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])# printing initial arrayprint("initial_array : ", str(ini_array));# Array to be added as rowrow_to_be_added = np.array([1, 2, 3])# Adding row to numpy arrayresult = np.vstack ((ini_array, row_to_be_added) )# printing resultprint ("resultant array", str(result)) |
Output:
initial_array : [[ 1 2 3] [45 4 7] [ 9 6 10]] resultant array [[ 1 2 3] [45 4 7] [ 9 6 10] [ 1 2 3]]
Sometimes we have an empty array and we need to append rows in it. Numpy provides the function to append a row to an empty Numpy array using numpy.append() function.
Syntax : numpy.append(arr, values, axis=None)
Case 1: Adding new rows to an empty 2-D array
- Python3
# importing Numpy packageimport numpy as np # creating an empty 2d array of int typeempt_array = np.empty((0,2), int)print("Empty array:")print(empt_array)# adding two new rows to empt_array# using np.append()empt_array = np.append(empt_array, np.array([[10,20]]), axis=0)empt_array = np.append(empt_array, np.array([[40,50]]), axis=0)print("\nNow array is:")print(empt_array) |
Empty array: [] Now array is: [[10 20] [40 50]]
Case 2: Adding new rows to an empty 3-D array
- Python3
# importing Numpy packageimport numpy as np # creating an empty 3d array of int typeempt_array = np.empty((0,3), int)print("Empty array:")print(empt_array)# adding three new rows to empt_array# using np.append()empt_array = np.append(empt_array, np.array([[10,20,40]]), axis=0)empt_array = np.append(empt_array, np.array([[40,50,55]]), axis=0)empt_array = np.append(empt_array, np.array([[40,50,55]]), axis=0)print("\nNow array is:")print(empt_array) |
Empty array: [] Now array is: [[10 20 40] [40 50 55] [40 50 55]]
Case 3: Adding new rows to an empty 4-D array
- Python3
# importing Numpy packageimport numpy as np # creating an empty 4d array of int typeempt_array = np.empty((0,4), int)print("Empty array:")print(empt_array)# adding four new rows to empt_array# using np.append()empt_array = np.append(empt_array, np.array([[100,200,400,888]]), axis=0)empt_array = np.append(empt_array, np.array([[405,500,550,558]]), axis=0)empt_array = np.append(empt_array, np.array([[404,505,555,145]]), axis=0)empt_array = np.append(empt_array, np.array([[44,55,550,150]]), axis=0)print("\nNow array is:")print(empt_array) |
Empty array: [] Now array is: [[100 200 400 888] [405 500 550 558] [404 505 555 145] [ 44 55 550 150]]
Last Updated on November 13, 2021 by admin