Swift extension that gives Dictionaries support for .map

dictionary_map.swift

extension Dictionary /* <KeyType, ValueType> */ {

    func mapKeys<U> (transform: KeyType -> U) -> Array<U> {
        var results: Array<U> = []
        for k in self.keys {
            results.append(transform(k))
        }
        return results
    }

    func mapValues<U> (transform: ValueType -> U) -> Array<U> {
        var results: Array<U> = []
        for v in self.values {
            results.append(transform(v))
        }
        return results
    }

    func map<U> (transform: ValueType -> U) -> Array<U> {
        return self.mapValues(transform)
    }

    func map<U> (transform: (KeyType, ValueType) -> U) -> Array<U> {
        var results: Array<U> = []
        for k in self.keys {
            results.append(transform(k as KeyType, self[ k ] as ValueType))
        }
        return results
    }

    func map<K: Hashable, V> (transform: (KeyType, ValueType) -> (K, V)) -> Dictionary<K, V> {
        var results: Dictionary<K, V> = [:]
        for k in self.keys {
            if let value = self[ k ] {
                let (u, w) = transform(k, value)
                results.updateValue(w, forKey: u)
            }
        }
        return results
    }

}

usage.swift

// key, value in dictionary
[ 0: 1, 2: 5, 8: 10 ].map({ (k, v) in k + v }) // -> [ 1, 7, 18 ]

// value in dictionary
[ 0: 1, 2: 5, 8: 10 ].map({ v in v * 2 }) // -> [ 1, 10, 20 ]

// key, value in dictionary to dictionary
[ 0: 1, 2: 5, 8: 10 ].map({ (k, v) in (v, k) }) // -> [ 1: 0, 5: 2, 10: 8 ]

Just paste it in the playground to play with it :)

Yes. In my opinion they should have choose something in the #(a: String) -> String { s } form, but it’s very succinct anyway.

👍

@jmnavarro That’s very old code! What are you looking at?! :P