Swift - Sort and array with [String: Int]

Question

I'm new with swift langage and I'm trying to code a function which permits to get the 6 most popular people on my Firebase Database.

I wrote an observer which place users in an array like that:

[[userID: numberOfFollowers], [userID: numberOfFollowers], ...]

I would like to keep only the 6 users with the highest number of followers.

Do you know if it is possible?

var people = [[String: Int]]()

func loadPeople() {
  var REF_FOLLOWERS = Database.database().reference().child("followers")

  REF_FOLLOWERS.observe(.value, with: { (snapshot: DataSnapshot!) in
     print("Got snapshot")
     if let dict = snapshot.value as? [String: Any] {
        for (key, value) in dict {
           var count = 1
           if let array = value as? [String: Any] {
              for _ in array {
                 count += 1
              }
           }

           self.people.append([key : count])
           self.tableView.reloadData()
        }
     }
  })
}

That's a database. Why don't you sort the items while fetching? — vadian
– vadian, Commented Feb 8, 2018 at 16:45

rushisangani · Accepted Answer · 2018-02-08 16:44:41Z

3

You could use something like:

var REF_FOLLOWERS = Database.database().reference().child("followers").queryOrdered(byChild: "numberOfFollowers").queryLimited(toFirst: 6).observe(.value, with: { (snapshot: DataSnapshot!) in {
}

This would give top 6 with the highest number of followers.

answered Feb 8, 2018 at 16:44

rushisangani

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3 Comments

Duncan C Over a year ago

This seems like the best solution. Why ask the database for ALL followers, then sort them every time they change. The database has query ordering and limiting built in, so why not use it? (voted)

Frank van Puffelen Over a year ago

The only thing you'll have to change is to get only the last 6, since sorting is always ascending in Firebase: queryLimited(toLast: 6). Btw that also means that you'll have to reverse the items on the client, typically by adding each subsequent one to the start of the view (instead of adding to the end).

KevinB Over a year ago

My problem is that I don't have a value "numberOfFollowers" in my DataBase. Should I create a new child in order to increment a counter for each user ?

Milan Nosáľ · Accepted Answer · 2018-02-08 16:42:58Z

0

REF_FOLLOWERS.observe(.value, with: { (snapshot: DataSnapshot!) in
   print("Got snapshot")
   if let dict = snapshot.value as? [String: Any] {
      for (key, value) in dict {
         var count = 1
         if let array = value as? [String: Any] {
            for _ in array {
               count += 1
            }
         }

         self.people.append([key : count])
      }
   }
   // this line will sort them and return first 6
   self.people = self.people.sorted(by: { $0["numberOfFollowers"] ?? 0 > $1["numberOfFollowers"] ?? 0}).prefix(6)
   // reload data just once at the end - be efficient!
   self.tableView.reloadData()
})

answered Feb 8, 2018 at 16:42

Milan Nosáľ

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