I have an app with an array of models that contain number fields. I'd like to be able to sum any given data field. I can do so with map by using the data field name ($0.cups for example). However I would like to programmatically send in a variable for "cups" and nothing I have tried works.
Here's some example code. I'd like to pass the field name that I want to total into the function sumOnAttribute
struct ContentView: View {
@State private var answer: String = ""
@State private var startingModels = [
StartingModel(name: "abe", age: 1, bags: 2, cups: 3),
StartingModel(name: "abe", age: 11, bags: 12, cups: 13),
StartingModel(name: "abe", age: 21, bags: 22, cups: 23),
StartingModel(name: "donna", age: 31, bags: 32, cups: 33),
StartingModel(name: "elsie", age: 41, bags: 42, cups: 43),
StartingModel(name: "farah", age: 51, bags: 52, cups: 53)
]//some data
var body: some View {
VStack(spacing: 10) {
Text("Do Some Math")
.font(.title)
Text(answer)
.font(.headline)
Button {
answer = String(sumOnAttribute(filterField: "abe", sumField: "cups"))
} label: {
Text("Make it So")
}
.font(.system(size: 20))
}//v
}//body
func sumOnAttribute(filterField: String, sumField: String) -> Double {
let filteredAttribute = startingModels.filter({ $0.name == filterField })
//$0.sumField does not work, $0.value(sumField) does not work
let nums = filteredAttribute.map({ $0.cups })
let total = nums.reduce(0, )
return total
}
}//struct
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
struct StartingModel: Identifiable {
let id = UUID()
let name: String
let age: Double
let bags: Double
let cups: Double
}//model
Seems like this should be simple, but I have not found any answer in a lot of searches. Any guidance would be appreciated. Xcode 13.3, iOS 15.4
CodePudding user response:
One option is a KeyPath
-- it's not a String
like you're using, but rather a compile-time-safe path to the property you're looking for. An implementation might look like this:
struct ContentView: View {
@State private var answer: String = ""
@State private var startingModels = [
StartingModel(name: "abe", age: 1, bags: 2, cups: 3),
StartingModel(name: "abe", age: 11, bags: 12, cups: 13),
StartingModel(name: "abe", age: 21, bags: 22, cups: 23),
StartingModel(name: "donna", age: 31, bags: 32, cups: 33),
StartingModel(name: "elsie", age: 41, bags: 42, cups: 43),
StartingModel(name: "farah", age: 51, bags: 52, cups: 53)
]//some data
var body: some View {
VStack(spacing: 10) {
Text("Do Some Math")
.font(.title)
Text(answer)
.font(.headline)
Button {
answer = String(sumOnAttribute(filterField: "abe", sumField: \.cups))
} label: {
Text("Make it So")
}
.font(.system(size: 20))
}//v
}//body
func sumOnAttribute(filterField: String, sumField: KeyPath<StartingModel,Double>) -> Double {
let filteredAttribute = startingModels.filter({ $0.name == filterField })
return filteredAttribute.map({ $0[keyPath:sumField] }).reduce(0, )
}
}//struct
If you really wanted to use a String
, you could consider using @dynamicMemberLookup
: https://www.hackingwithswift.com/articles/55/how-to-use-dynamic-member-lookup-in-swift
CodePudding user response:
not clear what you want, maybe you could try something like this, "...to pass the field name that I want to total into the function sumOnAttribute...":
struct ContentView: View {
@State private var namefield: String = "" // <-- here
@State private var sumfield: String = "" // <-- here
@State private var answer: String = ""
@State private var startingModels = [
StartingModel(name: "abe", age: 1, bags: 2, cups: 3),
StartingModel(name: "abe", age: 11, bags: 12, cups: 13),
StartingModel(name: "abe", age: 21, bags: 22, cups: 23),
StartingModel(name: "donna", age: 31, bags: 32, cups: 33),
StartingModel(name: "elsie", age: 41, bags: 42, cups: 43),
StartingModel(name: "farah", age: 51, bags: 52, cups: 53)
]
var body: some View {
VStack(spacing: 10) {
TextField("name field", text: $namefield).border(.red) // <-- here
TextField("sum field", text: $sumfield).border(.red) // <-- here
Text("Do Some Math")
.font(.title)
Text(answer)
.font(.headline)
Button {
answer = String(sumOnAttribute(filterField: namefield, sumField: sumfield)) // <-- here
} label: {
Text("Make it So")
}
.font(.system(size: 20))
}
}
func sumOnAttribute(filterField: String, sumField: String) -> Double {
let filteredAttribute = startingModels.filter{ $0.name == filterField }
// -- here
var nums: [Double] = []
switch sumField {
case "cups": nums = filteredAttribute.map{ $0.cups }
case "bags": nums = filteredAttribute.map{ $0.bags }
case "age": nums = filteredAttribute.map{ $0.age }
default: break
}
return nums.reduce(0, )
}
}