Swift - Append to NSMutableDictionary - ios

Question

I am trying to append to an NSMutableDictionary with the following code:
let RSVPDirectory = NSMutableDictionary()
for i in 0..<self.RSVPs.count {
var tmp = self.RSVPs[i]
var firstLetter = String()
if(tmp["lastname"] is NSNull)
{
firstLetter = ((tmp["email"] as? NSString)?.substring(to: 1).uppercased())!
}
else
{
firstLetter = ((tmp["lastname"] as? NSString)?.substring(to: 1).uppercased())!
}
if RSVPDirectory[firstLetter] == nil {
RSVPDirectory[firstLetter] = [AnyHashable]()
}
RSVPDirectory[firstLetter] = tmp
}
My problem with this is that I am expecting multiple tmp inside RSVPDirectory[firstLetter] but it only adds the first one as if its overriding the previous tmp
How do I append to NSMutableDictionary in swift, I know in objective-c you can do this:
[[RSVPDirectory objectForKey:firstLetter] addObject:tmp];
What would be the equivalent to that in swift?

Answer 1

Try the below code in a playground you will see the output, hope this gives you an idea.
func upperCaseFirstLetter(_ str: String) -> String {
guard let first = str.first else { return "" }
return "\(first)".uppercased()
}
var RSVPs = [[String:String]]()
var RSVPDirectory = [String: [[String:String]]]()
//Test Data
var str = ["email":"test1#c.com"]
RSVPs.append(str)
str = ["lastname":"Atest2"]
RSVPs.append(str)
for i in 0..<RSVPs.count {
var tmp = RSVPs[i]
var firstLetter = ""
if(tmp["lastname"] == nil) {
firstLetter = upperCaseFirstLetter(tmp["email"]!)
} else {
firstLetter = upperCaseFirstLetter(tmp["lastname"]!)
}
if RSVPDirectory[firstLetter] == nil {
RSVPDirectory[firstLetter] = [[String:String]]()
}
RSVPDirectory[firstLetter]?.append(tmp)
}
print(RSVPDirectory)

Answer 2

This is the native Swift version of your Objective-C-ish code.
It uses the Dictionary(grouping API of Swift 4
let RSVPDirectory = Dictionary(grouping: RSVPs) { (dictionary) -> String in
if let lastName = dictionary["lastname"] as? String {
return String(lastName.prefix(1).uppercased())
} else if let email = dictionary["email"] as? String {
return String(email.prefix(1).uppercased())
} else {
return "🚫"
}
}

Answer 3

Yes you are actually replacing the RSVPDirectory[firstLetter], overriding it every time with new tmp.
What you are looking for is this:
//RSVPDirectory[firstLetter] = tmp //Replace this line with below code
let tempArray = RSVPDirectory[firstLetter] as? [AnyHashable]
tempArray?.append(tmp)
RSVPDirectory[firstLetter] = tmpArray
Here I have used a tempArray because we want to mutate the array. Accessing it directly and trying to append new value will in-turn try to mutate an immutable value. So first I have got the array in the tempArray and then after mutating the array I swapped it back in the dictionary with updated values.