Python | Ways to add row/columns in numpy array
Last Updated : 22 Mar, 2023
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Given a Numpy array, the task is to add rows/columns basis on requirements to the Numpy array. Let's see a few examples of this problem in Python.
Add columns in the Numpy array
Method 1: Using np.append()
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# printing initial array
print("initial_array : ", str(ini_array));
# Array to be added as column
column_to_be_added = np.array([[1], [2], [3]])
# Adding column to array using append() method
arr = np.append(ini_array, column_to_be_added, axis=1)
# printing result
print ("resultant array", str(arr))
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 np.concatenate
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# Array to be added as column
column_to_be_added = np.array([[1], [2], [3]])
# Adding column to array using append() method
arr = np.concatenate([ini_array, column_to_be_added], axis=1)
# printing result
print ("resultant array", str(arr))
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 3: Using np.insert()
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# Array to be added as column
column_to_be_added = np.array([[1], [2], [3]])
# Adding column to array using append() method
arr = np.insert(ini_array, 0, column_to_be_added, axis=1)
# printing result
print ("resultant array", str(arr))
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 4: Using np.hstack()
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# Array to be added as column
column_to_be_added = np.array([1, 2, 3])
# Adding column to numpy array
result = np.hstack((ini_array, np.atleast_2d(column_to_be_added).T))
# printing result
print ("resultant array", str(result))
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Method 5: Using np.column_stack()
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# Array to be added as column
column_to_be_added = np.array([1, 2, 3])
# Adding column to numpy array
result = np.column_stack((ini_array, column_to_be_added))
# printing result
print ("resultant array", str(result))
Output:
resultant array [[ 1 2 3 1] [45 4 7 2] [ 9 6 10 3]]
Add row in Numpy array
Method 1: Using np.r_
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# printing initial array
print("initial_array : ", str(ini_array));
# Array to be added as row
row_to_be_added = np.array([1, 2, 3])
# Adding row to numpy array
result = np.r_[ini_array,[row_to_be_added]]
# printing result
print ("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]]
Method 2: Using np.insert
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# Array to be added as row
row_to_be_added = np.array([1, 2, 3])
#last row
row_n = arr.shape[0]
arr = np.insert(ini_array,row_n,[row_to_be_added],axis= 0)
# printing result
print ("resultant array", str(arr))
Output:
resultant array [[ 1 2 3] [45 4 7] [ 9 6 10] [ 1 2 3]]
Method 3: Using np.vstack()
import numpy as np
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
# Array to be added as row
row_to_be_added = np.array([1, 2, 3])
# Adding row to numpy array
result = np.vstack ((ini_array, row_to_be_added) )
# printing result
print ("resultant array", str(result))
Output:
resultant array [[ 1 2 3] [45 4 7] [ 9 6 10] [ 1 2 3]]
Method 4: Using numpy.append()
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.
Example 1: Adding new rows to an empty 2-D array
# importing Numpy package
import numpy as np
# creating an empty 2d array of int type
empt_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]]
Example 2: Adding new rows to an empty 3-D array
# importing Numpy package
import numpy as np
# creating an empty 3d array of int type
empt_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]]
Example 3: Adding new rows to an empty 4-D array
# importing Numpy package
import numpy as np
# creating an empty 4d array of int type
empt_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]]
