Cleaner way to filter nil in Swift array

Question

Let's say I have a Swift object called Animal. I have an array of Animal objects, some of which could be nil.

Currently I'm doing this:

arrayOfAnimal.filter({$0 != nil}) as! [Animal]

This feels rather hacky because of the force unwrapping. Wondering if there's a better way to filter out nils.

Your aim is to exclude all the nil values? – Mo Abdul-Hameed Dec 15 '17 at 20:02 — Mo Abdul-Hameed, Dec 15 '17 at 20:02

Martin R · Accepted Answer · 2018-12-11T20:52:29.580

54

flatMap() does the job:

let filtered = arrayOfAnimal.flatMap { $0 }

The closure (which is the identity here) is applied to all elements, and an array with the non-nil results is returned. The return type is [Animal] and no forced cast is needed.

Simple example:

let array: [Int?] = [1, nil, 2, nil, 3]
let filtered = array.flatMap { $0 }

print(filtered)            // [1, 2, 3]
print(type(of: filtered))  // Array<Int>

For Swift 4.1 and later, replace flatMap by compactMap.

edited Dec 11 '18 at 20:52

answered Dec 15 '17 at 20:08

Martin R

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I would use compactMap instead, since flatMap is now depreciated on Swift 4.0. – pierre23 Dec 10 '18 at 21:00

score 16 · Answer 2 · edited Feb 12 '20 at 12:55

16

Your code works, but there is a better way. Use the compactMap function.

struct Animal {}

let arrayOfAnimal: [Animal?] = [nil, Animal(), Animal(), nil]
let newArray: [Animal] = arrayOfAnimal.compactMap { $0 }

edited Feb 12 '20 at 12:55

koen

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answered Dec 15 '17 at 20:10

picciano

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yes, flatMap is deprecated – Vadim Kurochkin Nov 14 '20 at 10:02
This is now the correct answer – Julius Apr 17 '23 at 17:05

Cleaner way to filter nil in Swift array

2 Answers2