filter dictionary of type [String: [object]] for specific key in object arrays - swift

Question

I'm showing users a tableview that looks like the contacts view in the sense that the data source is a dictionary of type [String: [User]] and so I'm showing section headers with the first letter of the Users name.
Now, I want to allow them to search by the users first name... but I can't get this to work.
These are the dictionaries... the friends will hold data like this ["A" :[Users whose first name start with an A]] and so on
var friends = [String: [User]]()
var filteredFriends = [String: [User]]()
This is my filtering code with searchText being the first name I want to search by
self.filteredFriends = self.friends.filter{friend in
return friend.firstName.lowercased().contains(searchText)}
What I want to do is make filteredFriends have all of the values of friends whose users first names start with the text.
How do I make this work with a dictionary like mine?
Thanks
More Info:
Class User {
var firstName: String?
init(name: String){
self.firstName = name
}
}
Sample scenario:
friends = ["A" : [User(name: "Anthony), User(name: "Arnold")], "B" : [User(name: "Barry")]]
filteredFriends = friends
searchText = "an"
Desired filteredFriends (end result) = ["A" : [User(name: "Anthony)]]

Answer 1

There's no simple way. You just have to cycle through the whole dictionary, like this:
// these are your initial conditions
class User {
let firstName: String
init(name: String) {
self.firstName = name
}
}
let friends : [String:[User]] =
["A" : [User(name: "Anthony"), User(name: "Arnold")],
"B" : [User(name: "Barry")]]
let searchText = "an"
// and here we go...
var filteredFriends = [String:[User]]()
for entry in friends {
let filt = entry.value.filter{$0.firstName.lowercased().hasPrefix(searchText)}
if filt.count > 0 {
filteredFriends[entry.key] = filt
}
}
Now filteredFriends contains the desired result.

Answer 2

Ideally, you would use map to transform the input dictionary to the output dictionary, by filtering each of its values (User arrays). Unfortunately, Dicationary.map returns [(Key, Value)] (an array of `(Key, Value) tuples), not a new Dictionary. I'll take the more conventional, iterative approach instead.
Note: For those who are about to circle jerk around using functional styles everywhere, who are about to suggest using reduce: no. Pull out a profiler, and look at how slow and power-consuming it is to generate dictionaries with reduce. Especially important on a mobile device with limited battery.
Here's how I would do it:
let allFriends = [String: [User]]()
var filteredFriends = [String: [User]]()
let searchText = "a".lowercased()
for (initial, allFriendsWithInitial) in allFriends {
if initial.lowercased() == searchText {
// don't even have to bother filtering `friends`
filteredFriends[initial] = allFriendsWithInitial
}
let filteredFriendsWithInitial = allFriendsWithInitial.filter{
$0.firstName.lowercased().contains(searchText)
}
if !filteredFriendsWithInitial.isEmpty {
filteredFriends[initial] = filteredFriendsWithInitial
}
}
print(filteredFriends)