Filter, Map, Reduce, CompactMap, FlatMap - Swift - iOS Dev Interview Questions

Go to squarespace.com/seanallen to save 10% off your first purchase of a website or domain using code SEANALLEN.
Explaining Filter, Map and Reduce in Swift is a very common iOS Dev interview question. In this tutorial I'll walk you through how Filter, Map and Reduce work and how to chain them together for more complex examples. I also show you how compact map and flat map work.
This tutorial was created using Xcode 14 and iOS 16.
iOS Developer Interview Questions Playlist:
• Swift Interview Tips
My iOS Dev Courses:
seanallen.teachable.com/
My Closures Video:
• Swift Closures Explained
Twitter:
Sean Allen - / seanallen_dev
Hired.com:
hired.com/x/1n01g
Book and learning recommendations that help out the channel if you decide to purchase (Affiliate Links):
Paul Hudson's Hacking With Swift:
gumroad.com/a/762098803
Donny Wals - Combine:
gumroad.com/a/909014131
Mark Moeyken’s SwiftUI Books:
www.bigmountainstudio.com/swiftui-views-book/fzc51
Objc.io Books (Thinking in SwiftUI & Advanced Swift):
gumroad.com/a/656585843
#swift #softwaredeveloper #iosdeveloper
Timestamps:
0:00 - Filter, Map, Reduce
0:45 - Filter
3:02 - Map
4:35 - Reduce (simple)
6:05 - Reduce (on property)
7:17 - Chaining
10:18 - Compact Map
11:21 - Flat Map

[@DaveDDD]

The way you explained trailing closures in this made something finally click in my brain! I have no idea how it was able to confuse me for so long - it’s just so simple. Thank you!

[@seanallen]

I remember that feeling! Happy to help.

[@iLoveAppl3947]

Finally this video clicked for me... Simple examples makes you understand... i have watched 3 other videos across TH-cam to understand high order functions but they had stupid azz examples i couldn't understand a freking thing...

[@seanallen]

Glad it finally clicked!

[@kdtechniquesofficial6153]

Never knew about a reduce, just learned it today. Thanks, sean. I've been doing it the hard way all this time.

[@tylerwatt5651]

Thank you so much for putting this together! Especially for map and reduce!

[@ellen_kapii]

Excellent explanation, as usual. Thank you!

[@gakkieNL]

You can use keypaths with these high level functions. Makes for great readability!

[@milanfdl1968]

Cool video. Learned some new things today. Thank you!

[@mahmoudhashim3720]

Big Love Sean, THANK YOU, you and Afraz are the best

[@bosch5053]

Thanks

[@ANILAVCI]

Thanks for the shares. You have many followers from Turkey. Even though I watch with automatic subtitles, I learn a lot.

[@soheilpakgohar6630]

Great job Sean, before this I really got stuck which one is

[@JasonMitchellAZ]

Great explanations for these

[@Rayana_rei]

smart explanation, clear language! very efficient.. very.. ! 👏🏻

[@viniciushenriquepellegrini3534]

Amazing !

[@paulcristo]

Thanks.

[@seanallen]

Happy to help!

[@Patrick462]

Great explanations, really appreciate it.
A few reactions if you're open to such things:
1. Using Double for currency values will work 99.99% of the time. It's that .01% that will drive you crazy.
2. I wouldn't use the for loop as a tool to explain filter/map/reduce. Your original explanation is great and more than sufficient. Adding discussion of the for loop way of calculating will confuse a certain percent of viewers, and slow down almost everyone.

[@mario_luis_dev]

I disagree. He’s right in bringing up the for loop for comparisons, since that is the whole point on declarative programming: streamline the uglier, more verbose imperative style

[@filipecanzi]

Thanks Sean!!

[@MegaOlzo]

Thanks!)

[@efecetin5351]

You are amazing!

[@seanallen]

I appreciate the kind words :)

[@ahmednemo5954]

Amazing you are the best,Thanks for being one of the best is swift 👍

[@seanallen]

Thanks for the kind words, Ahmed.

[@xfabiosoft]

How about Zip? How does it work and when is useful?

[@filipchwastowski4228]

cool vid, but I believe that $0 and $1 when reducing does not refer to "this and next iteration", but to "current result and current iteration" - isn't that right? :) because here you keep handling constantly "accumulating current result" with each collection's element.

[@Jacob-rm7vo]

Yes that is how I understood reduce, even in other languages. It would accumulate - add the first and second, then add the third to that value. I think of $0 meaning lhs (left hand side) and $1 rhs

[@joshuascorca550]

@@Jacob-rm7vo exactly. Filter iterates through the array, doing this:
sumSoFar += object.numberToAdd
So $0 is the lhs, and $1 is the object on the rhs. This is why Sean needs to write $1.users and not $0.users. $0 is an Int already.

[@mkhasson97]

Awesome 🎉
Is there any plan for portfolio review? I’d love to hear your opinion about my website.
Thank you in advance 😊

[@victorriurean]

nice

[@guitaripod]

69th like

[@tigran.zakaryan]

thank you!