swift - sort an array of objects by their optional boolean property without force unwrapping

Question

I can sort this array of store objects by their \'flagship\' boolean property, but how can I safely unwrap the \'flagship\' property first?

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Answer 1

To filter nil values just use compactMap before sort

let flagshipStores = self.stores.compactMap { return $0.flagship }.sorted {
    $0 && !$1
}

Answer 2

How about:

$0.flagship == true && $1.flagship != true

The left side will succeed if the value is not nil and is true, the right side will succeed if the value is either nil or false.

Answer 3

As mr.Fixit pointed out on a comment, the accepted answer doesn't fully work because it doesn't take care of nils. Here is the correct answer with an extra string sample.

SWIFT 4

for a boolean sorting

 let flagshipStores = self.stores.sorted(by: {
    guard let flagship0 = $0.flagship, let flagship1 = $1.flagship else { 

       if $0.flagship == nil && $1.flagship == nil || $0.flagship != nil &&  $1.flagship == nil{

          return true

       }
       else {

          return false

       }
    } 

    return ($0.flagship == $1.flagship || $0.flagship == true && $1.flagship == false ? true : false)


 })

for strings comparison sorting

 let stores = self.stores.sorted(by: {
    guard let store0 = $0.store, let store1 = $1.store else { 

       if $0.store == nil && $1.store == nil || $0.store != nil &&  $1.store == nil{

          return true

       }
       else {

          return false

       }
    } 

    return ( ($0.store)?.localizedStandardCompare($1.store!) == ComparisonResult.orderedAscending )

 })

Answer 4

Here's another approach.

You can use flatMap which will remove nil objects and unwrap those that are present. Then, the force unwrap will be safe to sort:

let flagshipStores = stores.flatMap({ return $0.flagship ? $0 : nil }).sort {
    $0.flagship! && !$1.flagship!
}

This will remove stores with a nil flagship from the array.

Answer 5

One more approach: turn the Bool? into an Int, then compare the Ints. You get to specify how a nil value compares to non-nil values.

For instance, this sorts nil values before both false and true:

stores.sort { Int($0.flagship ?? -1) < Int($1.flagship ?? -1) }

This sorts nil values after both false and true:

stores.sort { Int($0.flagship ?? 2) < Int($1.flagship ?? 2) }

You can use the same pattern to make nil compare the same as true or the same as false. It's up to you.

Answer 6

let flagshipStores = self.stores.sort {
    guard let flagship0 = $0.flagship, let flagship1 = $1.flagship else { return false }
    return flagship0 && !flagship1
}