Pull unique items & calculations from an array in SwiftUI - ios

Question

I'm trying to create a Metrics view in my SwiftUI app. I'm building this so I can track my poker sessions I play. Each Session model looks like this:
struct PokerSession: Hashable, Codable, Identifiable {
var id = UUID()
let location: String
let game: String
let stakes: String
let date: Date
let profit: Int
let notes: String
let imageName: String
let startTime: Date
let endTime: Date
In my Metrics View I would like to iterate through all of the sessions which are stored in an array of type: [PokerSession] that displays a List of all the unique locations and their corresponding profit totals. This is how my code looks right now, obviously not working because I'm getting duplicate locations:
List {
ForEach(viewModel.sessions) { location in
HStack {
Text(location.location)
Spacer()
Text("$500")
.bold()
.foregroundColor(.green)
}
}
.navigationBarTitle(Text("Profit by Location"))
}
Does anyone know how I can grab unique locations and calculate their total profit? Many thanks!

Answer 1

I'd define a new type to store your totals:
struct LocationProfit: Identifiable {
let id = UUID()
let location: String
let profit: Int
}
Then you can group all your sessions by location in a dictionary, transform the sessions into a sum of profits, then transform the location and profit totals into our LocationProfit structure.
let locationProfits = Dictionary(grouping: sessions) { element in
element.location
}.mapValues { sessionsGroupedByLocation -> Int in
sessionsGroupedByLocation
.map { $0.profit }
.reduce(0, +)
}.map { locationProfitPair in
LocationProfit(location: locationProfitPair.key, profit: locationProfitPair.value)
}
Just stuff the whole conversion into your viewModel and iterate over the locationProfits in your View.

Answer 2

You need to filter which will return a filtered array of your PokerSessions by location then you reduce the filtered array to get the sum of your profit like this:
viewModel.sessions.filter( { $0.location == location}).reduce(0) { $0 + $1.profit})
edit with use case assuming it is in USD:
Text("$\(viewModel.sessions.filter( { $0.location == location}).reduce(0) { $0 + $1.profit}))")
You could also turn it into a string by add .description to the end of it. If you only need to display the data to the user, and don't need it generally available to the app, this is the simplest way of doing it.

Answer 3

You can generate an array of unique locations like this:
Array(Set(viewModel.sessions.map { $0.location }))
Use this in your ForEach to iterate over the location strings.
EDIT
To calculate the total per location, you can simply query your existing data (as described in Yrb's answer):
viewModel.sessions.filter({ $0.location == location }).reduce(0) { $0 + $1.profit }
Since you already use a view model, I suggest to hide both the creation of the unique locations list and the total profit lookup inside the view model, which will make your UI code much cleaner and more readable.
Also, if you have a lot of PokerSession entries, I suggest to generate the data only once and cache it inside the view model, e.g. using a custom data model as described in Rob's answer (or even simpler by generating a dictionary which maps from location string to total profit). The good thing about abstracting the data access away inside the view model is that you can introduce the caching approach later, without changing the UI layer, since you will be able to keep the same access methods and just change their implementation.

Answer 4

My solution was borrowed from most of your responses, thank you for the feedback. Below is the final code that worked, was able to avoid creating a dictionary and instead relied on map and reduce.
List {
ForEach(viewModel.uniqueLocations, id: \.self) { location in
HStack {
Text(location)
Spacer()
Text("$" + "\(viewModel.sessions.filter({$0.location == location}).reduce(0) { $0 + $1.profit})")
.bold()
.foregroundColor(.green)
}
}
.navigationBarTitle(Text("Profit by Location"))
}