Unordered Equality Checking in Swift

hasSameElements(as:).swift

extension Sequence where Element: Hashable {
    /// Count the number of occurrences of each value in a sequence
    public func countFrequency() -> [Element: Int] {
        var result = [Element: Int]()
        for element in self {
            result[element, default: 0] += 1
        }
        return result
    }
    
    /// Check for sequence equality while ignoring order
    public func hasSameElements(as s2: Self) -> Bool {
        let freq1 = self.countFrequency()
        let freq2 = s2.countFrequency()
        return freq1 == freq2
    }
}

extension Collection where Element: Hashable {
    /// Check for collection equality while ignoring order
    public func hasSameElements(as c2: Self) -> Bool {
        guard self.count == c2.count else { return false }
        let freq1 = self.countFrequency()
        let freq2 = c2.countFrequency()
        return freq1 == freq2
    }
}