  # Python | Ways to sum a list of lists and return a list of sums

Arrays | NumPy | Python Methods and Functions

Let`s take a look at some methods for summing a list and a return list.

Method # 1: Using the Naive Method

 ` # Python code for demo ` ` # sum of the list of list ` ` # using a naive method `   ` # Declaring the initial list of the list ` ` L ` ` = ` ` [[` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `], ` ` [` ` 4 ` `, ` ` 5 ` ` , ` ` 6 ` `], ` `  [ 7 , 8 , 9 ]] ``   # Print list of list print ( "Initial List -" , str (L))   # Using the naive method res = list () for j in range  ( 0 , len (L [ 0 ])): tmp = 0 for i in range ( 0 , len (L)): tmp = tmp + L [i] [j] res.append (tmp)    # print result print ( "final list -" , str (res)) `

Exit :

` Initial List - [[1, 2, 3], [4, 5, 6], [7, 8, 9]] final list - [12, 15, 18] `

Method # 2: Using the NumPy Array

` # Python code for demonstration `
` # sum of the list list `
` # using array functions `

` import numpy as np `

`   # Announcement list start list List = np. array ([[ 1 , 2 , 3 ], `

` [ 4 , ` ` 5 ` `, ` ` 6 ` `], `

` [` ` 7 ` `, ` ` 8 ` `, ` ` 9 ` `]]) `

` # Print list of list `

` print ` ` (` ` "Initial List -" ` `, ` ` str ` ` (` ` List ` `)) `

` # Using sum `

` res ` ` = ` ` np. ` ` sum ` < code class = "plain"> ( ` List ` `, ` ` 0 ) `

`   # print result print ( "final list -" , str (res)) `

` ` Exit:

` Initial List - [[1 2 3] [4 5 6] [7 8 9]] final list - [12 15 18] `

Method # 3: Using ` zip () ` and list comprehension

 ` # Python code to demonstrate ` ` # sum of the list list using ` ` # zip and list comprehension ` ` `  ` # Declaring initial list of list ` ` List ` ` = ` ` [[` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `] , ` ` [` ` 4 , 5 , 6 ], `` [ 7 , 8 , 9 ]]   # Print list of list print ( "Initial List -" , str ( List ))   # Using the comprehension list res = [ sum (i) for i in zip ( * List )]    # print result print ( "final list -" , str (res)) `

Exit :

` Initial List - [[1, 2, 3], [4, 5, 6], [7, 8, 9]] final list - [12, 15, 18] `