如何从 Swift 的字典中获取特定索引处的键？

Question

I have a Dictionary in Swift and I would like to get a key at a specific index.

var myDict : Dictionary<String,MyClass> = Dictionary<String,MyClass>()

I know that I can iterate over the keys and log them

for key in myDict.keys{

    NSLog("key = \(key)")

}

However, strangely enough, something like this is not possible

var key : String = myDict.keys[0]

Why ?

Answer 1

That's because keys returns LazyMapCollection<[Key : Value], Key> , which can't be subscripted with an Int . One way to handle this is to advance the dictionary's startIndex by the integer that you wanted to subscript by, for example:

let intIndex = 1 // where intIndex < myDictionary.count
let index = myDictionary.index(myDictionary.startIndex, offsetBy: intIndex)
myDictionary.keys[index]

Another possible solution would be to initialize an array with keys as input, then you can use integer subscripts on the result:

let firstKey = Array(myDictionary.keys)[0] // or .first

Remember, dictionaries are inherently unordered, so don't expect the key at a given index to always be the same.

Answer 2

Swift 3 : Array() can be useful to do this .

Get Key :

let index = 5 // Int Value
Array(myDict)[index].key

Get Value :

Array(myDict)[index].value

Answer 3

Here is a small extension for accessing keys and values in dictionary by index:

extension Dictionary {
    subscript(i: Int) -> (key: Key, value: Value) {
        return self[index(startIndex, offsetBy: i)]
    }
}

Answer 4

You can iterate over a dictionary and grab an index with for-in and enumerate (like others have said, there is no guarantee it will come out ordered like below)

let dict = ["c": 123, "d": 045, "a": 456]

for (index, entry) in enumerate(dict) {
    println(index)   // 0       1        2
    println(entry)   // (d, 45) (c, 123) (a, 456)
}

If you want to sort first..

var sortedKeysArray = sorted(dict) { $0.0 < $1.0 }
println(sortedKeysArray)   // [(a, 456), (c, 123), (d, 45)]

var sortedValuesArray = sorted(dict) { $0.1 < $1.1 }
println(sortedValuesArray) // [(d, 45), (c, 123), (a, 456)]

then iterate.

for (index, entry) in enumerate(sortedKeysArray) {
    println(index)    // 0   1   2
    println(entry.0)  // a   c   d
    println(entry.1)  // 456 123 45
}

If you want to create an ordered dictionary, you should look into Generics.

Answer 5

From https://developer.apple.com/library/prerelease/ios/documentation/swift/conceptual/swift_programming_language/CollectionTypes.html :

If you need to use a dictionary's keys or values with an API that takes an Array instance, initialize a new array with the keys or values property:

let airportCodes = [String](airports.keys) // airportCodes is ["TYO", "LHR"]   
let airportNames = [String](airports.values) // airportNames is ["Tokyo", "London Heathrow"]

Answer 6

SWIFT 3. Example for the first element

let wordByLanguage = ["English": 5, "Spanish": 4, "Polish": 3, "Arabic": 2]

if let firstLang = wordByLanguage.first?.key {
    print(firstLang)  // English
}

Answer 7

In Swift 3 try to use this code to get Key-Value Pair (tuple) at given index:

extension Dictionary {
    subscript(i:Int) -> (key:Key,value:Value) {
        get {
            return self[index(startIndex, offsetBy: i)];
        }
    }
}

Answer 8

SWIFT 4

---

Slightly off-topic: But here is if you have an Array of Dictionaries ie: [ [String : String] ]

var array_has_dictionary = [ // Start of array

   // Dictionary 1

   [ 
     "name" : "xxxx",
     "age" : "xxxx",
     "last_name":"xxx"
   ],

   // Dictionary 2

   [ 
     "name" : "yyy",
     "age" : "yyy",
     "last_name":"yyy"
   ],

 ] // end of array


cell.textLabel?.text =  Array(array_has_dictionary[1])[1].key
// Output: age -> yyy

Answer 9

Here is an example, using Swift 1.2

var person = ["name":"Sean", "gender":"male"]
person.keys.array[1] // "gender", get a dictionary key at specific index 
person.values.array[1] // "male", get a dictionary value at specific index

Answer 10

I was looking for something like a LinkedHashMap in Java. Neither Swift nor Objective-C have one if I'm not mistaken.

My initial thought was to wrap my dictionary in an Array. [[String: UIImage]] but then I realized that grabbing the key from the dictionary was wacky with Array(dict)[index].key so I went with Tuples. Now my array looks like [(String, UIImage)] so I can retrieve it by tuple.0 . No more converting it to an Array. Just my 2 cents.