GroupBy.swift

//stolen from @publicextension
extension Sequence {

    func groupBy<T>(groupBy: (Iterator.Element) -> T) -> [T: [Iterator.Element]] {
        var result: [T: [Iterator.Element]] = [:]

        self.forEach { element in
            let groupKey = groupBy(element)
            result[groupKey] = (result[groupKey] ?? []) + [element]
        }

        return result
    }

}


let dict = [
    "test": "value",
    "a222": "value1",
    "test2": "value3",
]

let p = dict.groupBy(groupBy: { $0.0.characters.count })
print(p)

let g = dict.keys.groupBy(groupBy: { $0.characters.count })
print(g)