Python | Triple List Summation

There can be an application requirement to append elements of 2-3 lists to one list and perform summation. This kind of application has a potential to come into the domain of Machine Learning or sometimes in web development as well. Let’s discuss certain ways in which this particular task can be performed. 

Method #1 : Using + operator + sum() This can be easily done using the plus operator as it does the element addition at the back of list. Similar logic is extended in case of multiple lists. The summation is performed using sum(). 

Python3

# Python3 code to demonstrate
# Triple List Summation
# using + operator + sum()

# initializing lists
test_list1 = [1, 3, 5, 5, 4]
test_list2 = [4, 6, 2, 8, 10]
test_list3 = [7, 5, 2, 9, 11]

# printing original lists
print ("The original list 1 is : " + str(test_list1))
print ("The original list 2 is : " + str(test_list2))
print ("The original list 3 is : " + str(test_list3))

# using + operator + sum()
# Triple List Summation
test_list1 = sum(test_list1 + test_list2 + test_list3)

# printing result
print ("The summed and modified list is : " + str(test_list1))

Output : 

The original list 1 is : [1, 3, 5, 5, 4]
The original list 2 is : [4, 6, 2, 8, 10]
The original list 3 is : [7, 5, 2, 9, 11]
The summed and modified list is : 82

Time Complexity: O(n) where n is the number of elements in the list “test_list”. The + operator + sum() is used to perform the task and it takes O(n) time.
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”.

Method #2 : Using itertools.chain() + sum() The chain function can also be employed to perform this particular tasks as it uses the iterator to perform this and hence offers a better performance over the above method. The summation is performed using sum(). 

Python3

# Python3 code to demonstrate
# Triple List Summation
# using itertools.chain() + sum()
from itertools import chain

# initializing lists
test_list1 = [1, 3, 5, 5, 4]
test_list2 = [4, 6, 2, 8, 10]
test_list3 = [7, 5, 2, 9, 11]

# printing original lists
print ("The original list 1 is : " + str(test_list1))
print ("The original list 2 is : " + str(test_list2))
print ("The original list 3 is : " + str(test_list3))

# using itertools.chain() + sum()
# Triple List Summation
test_list1 = sum(list(chain(test_list1, test_list2, test_list3)))

# printing result
print ("The summed and modified list is : " + str(test_list1))

Output : 

The original list 1 is : [1, 3, 5, 5, 4]
The original list 2 is : [4, 6, 2, 8, 10]
The original list 3 is : [7, 5, 2, 9, 11]
The summed and modified list is : 82

Time Complexity: O(n*n*n), where n is the number of elements in the list “test_list”.
Auxiliary Space: O(1), constant extra space is required