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

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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] `

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