Map with Optional Unwrapping in Swift

Question

Say I had the below api :

func paths() -> [String?] {
    return ["test", nil, "Two"]
}

And I was using this in a method where I needed [String], hence I had to unwrap it using the simple map function. I'm currently doing :

func cleanPaths() -> [String] {
    return paths.map({$0 as! String})
}

Here, the force-cast will cause an error. So technically I need to unwrap the Strings in the paths array. I'm having some trouble doing this and seem to be getting silly errors. Can someone help me out here?

score 46 · Accepted Answer · edited Aug 13 '18 at 20:47

46

compactMap() can do this for you in one step:

let paths:[String?] = ["test", nil, "Two"]

let nonOptionals = paths.compactMap{$0}

nonOptionals will now be a String array containing ["test", "Two"].

Previously flatMap() was the proper solution, but has been deprecated for this purpose in Swift 4.1

edited Aug 13 '18 at 20:47

Allen

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answered Jun 30 '15 at 21:24

Brad Larson

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Kudos for digging this function from the trench of Swift's undocumented higher-order functions! – Code Different Jun 30 '15 at 21:27
1

@ZoffDino - Credit for this should belong to Airspeed Velocity: http://airspeedvelocity.net/2015/06/23/protocol-extensions-and-the-death-of-the-pipe-forward-operator/ who first pointed this out to me. – Brad Larson Jun 30 '15 at 21:29
I've been playing with Swift for 9 months and still couldn't find a complete list of higher order functions in the language. Apple has a lot to catch up on this front. – Code Different Jun 30 '15 at 21:30
[Optional `map()` here](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Reference/Swift_Optional_Enumeration/index.html#//apple_ref/doc/uid/TP40015225-CH1-DontLinkElementID_8), [Sequence here](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Reference/Swift_SequenceType_Protocol/index.html#//apple_ref/doc/uid/TP40015890-CH1-DontLinkElementID_27) – oisdk Jun 30 '15 at 22:25
Note: this works in Swift 2. For 1.2, use `return paths.filter({$0 != nil}).map({$0 as String!})` – SushiGrass Jacob Jul 01 '15 at 14:10

score 5 · Answer 2 · answered Jun 30 '15 at 21:24

5

You should filter first, and map next:

return paths.filter { $0 != .None }.map { $0 as! String }

but using flatMap as suggested by @BradLarson is a just better

answered Jun 30 '15 at 21:24

Antonio

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score 1 · Answer 3 · answered Jun 30 '15 at 21:23

1

Perhaps what you want to is a filter followed by a map:

func cleanPaths() -> [String] {
    return paths()
            .filter {$0 != nil}
            .map {$0 as String!}
}

let x = cleanPaths()
println(x) // ["test", "two"]

answered Jun 30 '15 at 21:23

Code Different

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score -1 · Answer 4 · answered Aug 30 '18 at 19:24

-1

let name = obj.value
name.map { name  in print(name)}

answered Aug 30 '18 at 19:24

Venu Gopal Tewari

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Map with Optional Unwrapping in Swift

4 Answers4