Python | Adding value to sublists
Last Updated :
31 Mar, 2023
Sometimes, we just have to manipulate a list of lists by appending a similar value to all the sublists. Using a loop for achieving this particular task can be an option but sometimes leads to sacrificing the readability of code. It is always wanted to have a oneliner to perform this particular task. Let’s discuss certain ways in which this can be done.
Method #1: Using list comprehension can be used to perform this particular task using a similar looping construct but in just a single line. This increases code readability.
Python3
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
print("The original list : " + str(test_list))
K = "GFG"
res = [[i, j, K] for i, j in test_list]
print("The list after adding element : " + str(res))
|
Output
The original list : [[1, 3], [3, 4], [6, 5], [4, 5]]
The list after adding element : [[1, 3, 'GFG'], [3, 4, 'GFG'], [6, 5, 'GFG'], [4, 5, 'GFG']]
Time complexity: O(n), where n is the number of elements in the original list (test_list).
Auxiliary space: O(n), as a new list (res) is created with the same number of elements as the original list.
Method #2 : Using list comprehension + “+” operator This method is quite similar to the above method, but the difference is that plus operator is used to add the new element to each sublist.
Python3
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
print("The original list : " + str(test_list))
K = "GFG"
res = [sub + [K] for sub in test_list]
print("The list after adding element : " + str(res))
|
Output
The original list : [[1, 3], [3, 4], [6, 5], [4, 5]]
The list after adding element : [[1, 3, 'GFG'], [3, 4, 'GFG'], [6, 5, 'GFG'], [4, 5, 'GFG']]
Time complexity: O(n) where n is the number of sublists in the test_list.
Auxiliary space: O(n) for the new list ‘res’ created using the list comprehension.
Method #3 : Using for loop
Python3
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
print("The original list : " + str(test_list))
K = "GFG"
res = []
for i in test_list:
i.append(K)
res.append(i)
print("The list after adding element : " + str(res))
|
Output
The original list : [[1, 3], [3, 4], [6, 5], [4, 5]]
The list after adding element : [[1, 3, 'GFG'], [3, 4, 'GFG'], [6, 5, 'GFG'], [4, 5, 'GFG']]
Time complexity: O(n), where n is the length of the input list.
Auxiliary space: O(n), where n is the length of the input list.
Method #4: Using map() and lambda function
Here is the approach using map() and lambda function
Python3
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
print("The original list : " + str(test_list))
K = "GFG"
res = list(map(lambda x: x + [K], test_list))
print("The list after adding element : " + str(res))
|
Output
The original list : [[1, 3], [3, 4], [6, 5], [4, 5]]
The list after adding element : [[1, 3, 'GFG'], [3, 4, 'GFG'], [6, 5, 'GFG'], [4, 5, 'GFG']]
Time complexity: O(n)
Auxiliary Space: O(n)
Method #5: Using itertools.chain and zip:
Python3
import itertools
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
K = "GFG"
print("The original list : " + str(test_list))
res = [list(itertools.chain(i, [K])) for i in test_list]
print("The list after adding element : " + str(res))
|
Output
The original list : [[1, 3], [3, 4], [6, 5], [4, 5]]
The list after adding element : [[1, 3, 'GFG'], [3, 4, 'GFG'], [6, 5, 'GFG'], [4, 5, 'GFG']]
Time complexity: O(n)
Auxiliary Space: O(n*k)
Method #6: Using numpy
To use numpy we need to install it first. You can install it using the following command: pip install numpy
Step by step approach:
- Import numpy module using import numpy as np
- Convert test_list into numpy array using np.array(test_list)
- Append the value ‘K’ to the numpy array using np.append()
- Reshape the numpy array to the original shape using .reshape() method
- Convert the numpy array back to list using .tolist() method
Python3
import numpy as np
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
print("The original list : " + str(test_list))
K = "GFG"
test_np = np.array(test_list)
res_np = np.append(test_np, np.full((len(test_list), 1), K), axis=1).reshape(len(test_list), -1).tolist()
print("The list after adding element : " + str(res_np))
|
Output:
The original list : [[1, 3], [3, 4], [6, 5], [4, 5]]
The list after adding element : [['1', '3', 'GFG'], ['3', '4', 'GFG'], ['6', '5', 'GFG'], ['4', '5', 'GFG']]
Time complexity: O(n) (where n is the number of elements in the list)
Auxiliary space: O(n) (for creating a numpy array)
Method #7: Using extend() method inside a for loop
Use a for loop to iterate through each sublist of the original list.
Use the extend() method to append the value to each sublist.
Python3
test_list = [[1, 3], [3, 4], [6, 5], [4, 5]]
K = "GFG"
for sublist in test_list:
sublist.extend([K])
print("The list after adding element : " + str(test_list))
|
Output
The list after adding element : [[1, 3, 'GFG'], [3, 4, 'GFG'], [6, 5, 'GFG'], [4, 5, 'GFG']]
Time complexity: O(n), where n is the length of the list.
Auxiliary space: O(1), because no additional data structure is created.
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