Swift 3 で Array から Dictionary に変換するサンプル

convertArrayToDictonary.swift

import Foundation

struct Person {
    
    var number: Int
    var name: String
    
}

let persons = [Person(number: 1, name: "John"),
               Person(number: 2, name: "Ken"),
               Person(number: 3, name: "Mike")]

let personDic = persons.reduce([Int: Person]()) { (result, person) in
    var newResult = result
    newResult[person.number] = person
    return newResult
}

let thirdPerson = personDic[3]
thirdPerson?.name   // Mike