Swift·Swift from optionals to SwiftUI

Collections

Use arrays, dictionaries and sets with map, filter and reduce.

Beginner 12 min read Lesson 3 of 300 Challenge included

What you will be able to do

Use arrays for ordered data.
Use dictionaries for keyed lookups.
Use sets for membership.
Prefer map and filter over manual loops.

In plain English

Arrays keep order, dictionaries map keys to values and sets hold unique values. Value semantics mean assignment copies the collection. Use map, filter, reduce and sorted for transformations.

Collections.swiftSwift

let lessons = ["HTML", "CSS", "SQL"]
let long = lessons.filter { $0.count >= 3 }
let lengths = lessons.map(\.count)
let total = lengths.reduce(0, +)
print(long, total)

Your turn

Filter a collection

Easy

Return only lessons whose name has at least three characters.

SWIFT · starter

lessons

Check your understanding before moving on.

Knowledge checkQuestion 1

Which collection stores unique values without order?

Select an answer to continue

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Lesson 3 of 300 · 0% of course