Swift dictionary keys

Question

I need to convert a Dictionary with mixed key keys to the same exact Dictionary , but with only lowercase keys.

Here is my attempt (it works, but I found this implementation extremely rude)

 extension Dictionary { func lowercaseKeys()->Dictionary<String, AnyObject>{ var newDictionary = Dictionary<String,AnyObject>() for k in keys{ if let k_string = k as? String{ newDictionary[k_string.lowercaseString] = self[k] as? AnyObject } } return newDictionary } } 

Can you suggest a more elegant way to solve this problem?

Answer 1

Changes own keys without using a temporary dictionary;)

 var dict = ["HEJ":"DÅ", "NeJ":"tack"] for key in dict.keys { dict[key.lowercaseString] = dict.removeValueForKey(key) } print(dict) 

[hej: DÅ, nej: tack]

EDIT

I made this extension, its a little dirty, but I will update it again.

 extension Dictionary { mutating func lowercaseKeys() { for key in self.keys { let str = (key as! String).lowercaseString self[str as! Key] = self.removeValueForKey(key) } } } var dict = ["HeJ":"Då", "nEJ":"taCK!"] dict.lowercaseKeys() print(dict) 

["hej": "Då", "nej": "taCK!" ]

EDIT 2

 extension Dictionary where Key: StringLiteralConvertible { mutating func lowercaseKeys() { for key in self.keys { self[String(key).lowercaseString as! Key] = self.removeValueForKey(key) } } } var dict = ["NamE":"David", "LAST_NAME":"Göransson"] dict.lowercaseKeys() // Will compile var dict2 = [0:"David", 0:"Göransson"] dict2.lowercaseKeys() // Won't compile because Key isn't StringLiteralConvertible 

Answer 2

Smth like that?

  var dict = ["KEY": "value"] var newDict = [String: AnyObject]() for (key, value) in dict { newDict[key.lowercaseString] = value } 

Answer 3

Arbitur answer updated for Swift 3:

 extension Dictionary where Key: ExpressibleByStringLiteral { public mutating func lowercaseKeys() { for key in self.keys { self[String(describing: key).lowercased() as! Key] = self.removeValue(forKey: key) } } } 

Answer 4

Here is my solution, without the use of force, is absolutely safe.

 protocol LowercaseConvertible { var lowercaseString: Self { get } } extension String: LowercaseConvertible {} extension Dictionary where Key: LowercaseConvertible { func lowercaseKeys() -> Dictionary { var newDictionary = Dictionary() for k in keys { newDictionary[k.lowercaseString] = self[k] } return newDictionary } } 

Answer 5

As an alternative to a loop, you can use the map function:

 func lowercaseKeys () -> Dictionary<String, AnyObject> { var newDictionary = Dictionary<String,AnyObject>() Array(keys).map { key in newDictionary[(key as! String).lowercaseString] = self[key] as? AnyObject } return newDictionary }