Ordered map in Swift

Question

Is there any built-in way to create an ordered map in Swift 2? Arrays [T] are sorted by the order that objects are appended to it, but dictionaries [K : V] aren't ordered.

For example

var myArray: [String] = []
myArray.append("val1")
myArray.append("val2")
myArray.append("val3")

//will always print "val1, val2, val3"
print(myArray)


var myDictionary: [String : String] = [:]
myDictionary["key1"] = "val1"
myDictionary["key2"] = "val2"
myDictionary["key3"] = "val3"

//Will print "[key1: val1, key3: val3, key2: val2]"
//instead of "[key1: val1, key2: val2, key3: val3]"
print(myDictionary)

Are there any built-in ways to create an ordered key : value map that is ordered in the same way that an array is, or will I have to create my own class?

I would like to avoid creating my own class if at all possible, because whatever is included by Swift would most likely be more efficient.

Answer 1

You can order them by having keys with type Int.

var myDictionary: [Int: [String: String]]? 

or

var myDictionary: [Int: (String, String)]? 

I recommend the first one since it is a more common format (JSON for example).

Answer 2

Just use an array of tuples instead. Sort by whatever you like. All "built-in".

var array = [(name: String, value: String)]() // add elements array.sort() { $0.name < $1.name } // or array.sort() { $0.0 < $1.0 } 

Answer 3

"If you need an ordered collection of key-value pairs and don’t need the fast key lookup that Dictionary provides, see the DictionaryLiteral type for an alternative." - https://developer.apple.com/reference/swift/dictionary

Answer 4

You can use KeyValuePairs, from documentation:

Use a KeyValuePairs instance when you need an ordered collection of key-value pairs and don’t require the fast key lookup that the Dictionary type provides.

let pairs: KeyValuePairs = ["john": 1,"ben": 2,"bob": 3,"hans": 4]
print(pairs.first!)

//prints (key: "john", value: 1)