Retrieve from firebase database calculating average - ios

Question

I'm creating an iOS application that uses placenames and rating for each place. I have already made the thing work. I mean that, I save data to my database and I also can read them. The only problem, is when I read them I want them to load on my tableviewcell, by calculating average for each place. See the screenshots and if you don't understand something, ask me to edit the answer.
TableView
Firebase
My Code that loads data to tableview
import UIKit
import FirebaseDatabase
class PlacesTableViewController: UITableViewController {
//MARK: Properties
#IBOutlet weak var placesTableView: UITableView!
var dbRef:FIRDatabaseReference?
var places = [Places]()
private var loadedLabels = [String: String]()
private var loadedRatings = [String: Int]()
override func viewDidLoad()
{
super.viewDidLoad()
dbRef = FIRDatabase.database().reference()
// Loads data to cell.
loadData()
}
override func numberOfSections(in tableView: UITableView) -> Int
{
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
//return the number of rows
return places.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
{
// Table view cells are reused and should be dequeued using a cell identifier.
guard let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath) as? PlacesTableViewCell else {
fatalError("The dequeued cell is not an instance of PlacesTableView Cell.")
}
let place = places[indexPath.row]
cell.placeLabel.text = place.name
cell.ratingControl.rating = place.rating
return cell
}
private func loadData()
{
dbRef!.observe(.childAdded, with: {
(placeSnapshot) in
//print("Adding place \(placeSnapshot.key)...")
let labels = placeSnapshot.childSnapshot(forPath: "placeLabel")
for (key, label) in labels.value as! [String: String] {
self.updatePlace(key, label: label)
}
let ratings = placeSnapshot.childSnapshot(forPath: "rating")
for (key, rating) in ratings.value as! [String: Int] {
self.updatePlace(key, rating: rating)
}
})
}
private func updatePlace(_ key: String, label: String? = nil, rating: Int? = nil)
{
if let label = label {
loadedLabels[key] = label
}
if let rating = rating {
loadedRatings[key] = rating
}
guard let label = loadedLabels[key], let rating = loadedRatings[key] else {
return
}
if let place = Places(name: label, rating: rating) {
places.append(place)
placesTableView.reloadData()
}
}
}
Places swift
import UIKit
class Places {
//MARK: Properties
var name: String
var rating: Int
//MARK:Types
struct PropertyKey {
static let name = "name"
static let rating = "rating"
}
//MARK: Initialization
init?(name: String, rating: Int) {
// Initialize stored properties.
self.name = name
self.rating = rating
// Initialization should fail if there is no name or if the rating is negative.
// The name must not be empty
guard !name.isEmpty else {
return nil
}
// The rating must be between 0 and 5 inclusively
guard (rating >= 0) && (rating <= 5) else {
return nil
}
}
}

Answer 1

As i understood you want to have a rounded double for your application and not a double. Just change the code inside your loadData() function and it would work for you. Also you will call updatePlace() as you did. Please approve Jay's answer, he wrote the code.
private func loadData()
{
dbRef!.observe(.childAdded, with: {
(placeSnapshot) in
let parentRef = self.dbRef?.child(placeSnapshot.key)
let ratingRef = parentRef?.child("rating")
ratingRef?.observe(.value, with: { snapshot in
let count = snapshot.childrenCount
var total: Double = 0.0
for child in snapshot.children {
let snap = child as! FIRDataSnapshot
let val = snap.value as! Double
total += val
}
let average = total/Double(count)
print("Average for \(placeSnapshot.key) = \(Int(round(average)))")
self.updatePlace("" , label: placeSnapshot.key, rating: Int(round(average)))
})
})
}

Answer 2

This is a pretty verbose answer but it will iterate over the child nodes of the rating node and calculate the average
let parentRef = self.dbRef.child("Paradosiako - Panorama")
let ratingRef = parentRef.child("rating") // rating node
ratingRef.observe(.value, with: { snapshot in
let count = snapshot.childrenCount
var total: Double = 0.0
for child in snapshot.children {
let snap = child as! FIRDataSnapshot
let val = snap.value as! Double
total += val
}
let average = total/Double(count)
print(average)
})
EDIT
To iterate over all the places and get the averages, here's the code
let placesRef = self.dbRef.child("akapnapp")
placesRef.observeSingleEvent(of: .value, with: { snapshot in
for child in snapshot.children {
let placeSnap = child as! FIRDataSnapshot
let ratingsSnap = placeSnap.childSnapshot(forPath: "rating")
let count = ratingsSnap.childrenCount
var total: Double = 0.0
for child in ratingsSnap.children {
print(child)
let snap = child as! FIRDataSnapshot
let val = snap.value as! Double
total += val
}
let average = total/Double(count)
print(average)
}
})
and the output showing the code works correctly. My child nodes were named a,b,c instead of the childByAutoId in the question but it works either way.
Snap (a) 3
Snap (b) 3
3.0
Snap (a) 2
Snap (b) 4
Snap (c) 5
3.67