{"id":3922,"date":"2021-01-27T16:20:17","date_gmt":"2021-01-27T16:20:17","guid":{"rendered":"https:\/\/www.gubatron.com\/blog\/?p=3922"},"modified":"2021-01-27T16:28:21","modified_gmt":"2021-01-27T16:28:21","slug":"python-in-functional-style-how-to-add-2-lists-of-integers-without-using-loops","status":"publish","type":"post","link":"https:\/\/www.gubatron.com\/blog\/python-in-functional-style-how-to-add-2-lists-of-integers-without-using-loops\/","title":{"rendered":"Python in Functional Style: How to add 2 lists of integers without using loops"},"content":{"rendered":"\r\n

Usually you’d add a list of integers this way:

<\/p>\r\n

[pastacode lang=”python” manual=”a%20%3D%20%5B2%2C%202%2C%202%2C%202%5D%0Ab%20%3D%20%5B2%2C%202%2C%202%2C%202%5D%0Ac%20%3D%20%5B%5D%0Afor%20i%20in%20range(len(a))%3A%0A%20c.append(a%5Bi%5D%20%2B%20b%5Bi%5D)” message=”” highlight=”” provider=”manual”\/]<\/p>\r\n

You can do it functionally without any loops in different ways:<\/p>\r\n



Using map and a lambda that adds them up<\/h4>\r\n

[pastacode lang=”python” manual=”c%20%3D%20list(map(lambda%20x%2Cy%3A%20x%2By%2C%20a%2C%20b))” message=”” highlight=”” provider=”manual”\/]<\/p>\r\n

or you can import the add<\/strong> operator as a named function<\/p>\r\n

[pastacode lang=”python” manual=”from%20operator%20import%20add%0Ac%20%3D%20list(map(add%2C%20a%2C%20b))” message=”” highlight=”” provider=”manual”\/]<\/p>\r\n


Ever zipped two lists into a list of tuples?

<\/h4>\r\n

There’s another more convoluted way if you want to play with “zip”.

\"Close
Imagine a jacket zipper and the teeth on each side of the zipper is one element on each one of the list.


When you zip the lists a<\/strong> and b<\/strong>, you end up with a list of tuples of matching elements from the given lists.<\/p>\r\n

[pastacode lang=”python” manual=”%3E%3E%3E%20list(zip(a%2Cb))%0A%5B(2%2C%202)%2C%20(2%2C%202)%2C%20(2%2C%202)%2C%20(2%2C%202)%5D” message=”” highlight=”” provider=”manual”\/]<\/p>\r\n

you could now map a function to add the elements within each tuple on that list.


<\/p>\r\n

[pastacode lang=”python” manual=”%3E%3E%3E%20list(map(lambda%20tup%3A%20tup%5B0%5D%2Btup%5B1%5D%2C%20zip(a%2Cb)))%0A%5B4%2C%204%2C%204%2C%204%5D” message=”” highlight=”” provider=”manual”\/]<\/p>\r\n


Notice how we don’t convert to list after zip, we can work directly with the zip iterator, we only convert to list with the final map iterator.

Python 2 & 3 Note:<\/strong>

In Python 2 it’s not necessary to use list()<\/strong>, the map() and zip() methods return lists there. But stay away from Python 2, a lot of projects are now discontinuing support.<\/p>\r\n","protected":false},"excerpt":{"rendered":"

Usually you’d add a list of integers this way: [pastacode lang=”python” manual=”a%20%3D%20%5B2%2C%202%2C%202%2C%202%5D%0Ab%20%3D%20%5B2%2C%202%2C%202%2C%202%5D%0Ac%20%3D%20%5B%5D%0Afor%20i%20in%20range(len(a))%3A%0A%20c.append(a%5Bi%5D%20%2B%20b%5Bi%5D)” message=”” highlight=”” provider=”manual”\/] You can do it functionally without any loops in different ways: Using map and a lambda that adds them up [pastacode lang=”python” manual=”c%20%3D%20list(map(lambda%20x%2Cy%3A%20x%2By%2C%20a%2C%20b))” message=”” highlight=”” provider=”manual”\/] or you can import the add operator as a named function [pastacode lang=”python” manual=”from%20operator%20import%20add%0Ac%20%3D%20list(map(add%2C%20a%2C%20b))” […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[15],"tags":[1639,1638,1634,1431,1635,1458,1637,1636],"class_list":["post-3922","post","type-post","status-publish","format-standard","hentry","category-code","tag-fp","tag-functional-programming","tag-iterators","tag-list","tag-map","tag-python","tag-python3","tag-zip"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p5Unzf-11g","jetpack-related-posts":[{"id":2568,"url":"https:\/\/www.gubatron.com\/blog\/bfs-vs-dfs-graph-search-algorithms-in-python\/","url_meta":{"origin":3922,"position":0},"title":"BFS vs DFS Graph Search Algorithms in Python","author":"gubatron","date":"November 15, 2011","format":false,"excerpt":"Here are implementations of iterative BFS and DFS search algorithms in Python. 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After coding in other languages, then going back to C++ and understanding at a lower level how references and pointers work, this was pretty easy to figure out. 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