Map array of objects to Dictionary in Swift

ios arrays swift dictionary

iOSGeek · Jul 19, 2016 · Viewed 66.5k times · Source

I have an array of Person's objects:

class Person {
   let name:String
   let position:Int
}

and the array is:

let myArray = [p1,p1,p3]

I want to map myArray to be a Dictionary of [position:name] the classic solution is:

var myDictionary =  [Int:String]()

for person in myArray {
    myDictionary[person.position] = person.name
}

is there any elegant way by Swift to do that with the functional approach map, flatMap... or other modern Swift style

Answer

Since Swift 4 you can do @Tj3n's approach more cleanly and efficiently using the into version of reduce It gets rid of the temporary dictionary and the return value so it is faster and easier to read.

Sample code setup:

struct Person { 
    let name: String
    let position: Int
}
let myArray = [Person(name:"h", position: 0), Person(name:"b", position:4), Person(name:"c", position:2)]

Into parameter is passed empty dictionary of result type:

let myDict = myArray.reduce(into: [Int: String]()) {
    $0[$1.position] = $1.name
}

Directly returns a dictionary of the type passed in into:

print(myDict) // [2: "c", 0: "h", 4: "b"]

Map array of objects to Dictionary in Swift

Answer

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