Swap keys and values of a Dictionary

Mar 24, 2021 • Rizwan • Dictionary

• swift, swift dictionary, dictionary

extension Dictionary where Value: Hashable {
    struct DuplicateValuesError: Error { }
    init?(swappingKeysAndValues dict: [Value:  Key]) {
        do {
            try self.init(dict.lazy.map { ($0.value, $0.key) },
                          uniquingKeysWith: { _,_ in throw DuplicateValuesError() })
        } catch {
            return nil
        }
    }
}

let dict = [1 : "A", 2 : "B", 3 : "C", 4 : "D", 5 : "E"]
if let swappedDict = Dictionary(swappingKeysAndValues: dict) {
    print(swappedDict)
}else{
    print("Unable to swap keys and values")
}

Result:
["A": 1, "D": 4, "C": 3, "E": 5, "B": 2]