How do I check in Swift if two arrays contain the same elements regardless of the order in which those elements appear in?

Question

Let\'s say there are two arrays...

var array1 = [\"a\", \"b\", \"c\"]
var array2 = [\"b\", \"c\", \"a\"]

I\'d like the result of the compar

Answer 1

If elements of your arrays are conforming to Hashable you can try to use the bag (it's like a set with the registration of each item amount). Here I will use a simplified version of this data structure based on Dictionary. This extension helps to create bag from array of Hashable:

extension Array where Element: Hashable {
    var asBag: [Element: Int] {
        return reduce(into: [:]) {
            $0.updateValue(($0[$1] ?? 0) + 1, forKey: $1)
        }
    }
}

Now you need to generate 2 bags from initial arrays and compare them. I wrapped it in this extension:

extension Array where Element: Hashable {
    func containSameElements(_ array: [Element]) -> Bool {
        let selfAsBag = asBag
        let arrayAsBag = array.asBag
        return selfAsBag.count == arrayAsBag.count && selfAsBag.allSatisfy {
            arrayAsBag[$0.key] == $0.value
        }
    }
}

This solution was tested with Swift 4.2/Xcode 10. If your current Xcode version is prior to 10.0 you can find the function allSatisfy of ArraySlice in Xcode9to10Preparation. You can install this library with CocoaPods.