Dictionary inside dictionary - ios

Question

I am trying to use a list that is a value for a dictionary key/pair set, and this dictionary is itself a value in a key/pair set in a dictionary. To explain, this is how I initialize it.
var dictOfEvents = [Int: [Int: [PFObject]]]()
I am trying to add events to the list, with the inner dictionary's key being the day of month and the outer one being the month. For example, an event on May 1 would be:
dictOfEvents[5:[1:[ListOfEvents]]
Where ListOfEvents is an array of PFObjects. Before I added the month functionality, and thus the outer dictionary, the way I added new events was:
` self.dictOfEvents[components.day] = [event]
But now, when I try to extend this with:
self.dictOfEvents[components.month]?[components.day]! = [event]
It does not work. Any explanation on how to create new event lists and access this double layer dictionary would be greatly appreciated.
(Note: I don't know where to put the ! and the ? in the last piece of code so please excuse me if I made a mistake.)

Answer 1

Here is what I think could be a good use of optionals in your case (and should respond to your question):
var dic: [Int: [Int: [String]]] = [:]
dic[5] = [1:["Hello", "World"]]
if let list = dic[5]?[1] {
// your list exist and you can safely use it
for item in list {
println(item)
}
}
I just used String instead of PFObject.
A different approach could be:
/*
Define a struct to encapsulate your Month and Day
Make it Hashable so that you can use it as Dictionary key
*/
public struct MonthDay: Hashable {
let month: Int
let day: Int
public var hashValue: Int { return month * 100 + day }
}
public func ==(lhs: MonthDay, rhs: MonthDay) -> Bool {
return lhs.month == rhs.month && lhs.day == rhs.day
}
var dictOfEvents = [MonthDay :[String]]()
let aMonthAndDay = MonthDay(month: 5, day: 1)
dictOfEvents[aMonthAndDay] = ["Hello", "World"]
if let list = dictOfEvents[aMonthAndDay] {
// your list exist and you can safely use it
for item in list {
println(item)
}
}

Answer 2

U can simple change:
self.dictOfEvents[components.month]?[components.day]! = [event]
to :
self.dictOfEvents[components.month]![components.day]! = [event]
Because Dictionary has subscript, Dictionary? doesn't have subscript.
if U try add Events to Dictionary. I suggest to use this:
var dictOfEvents = [Int: [Int: [PFObject]]]()
var dictOfDayEvents = [Int:[PFObject]]()
dictOfDayEvents.updateValue([PFObject()], forKey: 1)
dictOfEvents.updateValue(dictOfDayEvents, forKey: 5)