How to sum a particular key in an Array Object Swift 4? - ios

Question

This response from API:
{
"status": 200,
"message": "Success",
"data": {
"result": [
{
"name": "Anything",
"response": [
{
"name": "XYZ",
"prize": "1.86"
},
{
"name": "ABCD",
"prize": "9.86"
}
]
}
],
"overall": "XYZ"
}
}
How, can I sum the prize in the response as I have to show it in the header of Table. I did this.
var prizeArr = [Int]()
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView?
{
let header = tableView.dequeueReusableHeaderFooterView(withIdentifier: cellReuseIdentifier) as! OverallHeaderCell
let countArr = winnerArr![section]["response"] as? Array<Dictionary<String,Any>>
prizeArr = (countArr!.compactMap{ $0["prize"] })
print(prizeArr)
header.textL[0].text = winnerArr![section]["name"] as? String
header.textL[3].text = "\(String(describing: countArr!.count))"
return header
}
I am trying to store the prize in the prizeArr and then I will sum it up. But, it prints nil, but when I write it in the terminal it gives the value individually. How, can I sum the prize in this ArrayObject?
Also, when I use prizeArr = [String](), then it works and store the prize in the Array, but for Int why is it not working?

Answer 1

First, as #Benhamine pointed out you should start with a clean architecture and map your JSON into a type safe class.
Step 1: Codable Types
Lets define a structure that represents our JSON so we can better consume it in our App. JSON is something we never want to pass around our App. Lets rather pass around something well-defined and documented so we have no need to do any force unwraps and crash our App.
struct JSONResponse: Codable {
enum CodingKeys: String, CodingKey {
case data
}
let data: Data
}
extension JSONResponse {
struct Data: Codable {
enum CodingKeys: String, CodingKey {
case results = "result"
}
let results: [Result]
}
}
extension JSONResponse.Data {
struct Result: Codable {
let name: String
let winners: [Winner]
enum CodingKeys: String, CodingKey {
case winners = "response"
case name
}
}
}
extension JSONResponse.Data.Result {
struct Winner: Codable {
let name: String
let prize: String
}
}
Step 2: Parsing
Parsing using Codable is super simple. The code below will show how we convert it into JSON and also how one could go about getting the sum of the float values.
do {
let o: JSONResponse = try JSONDecoder().decode(JSONResponse.self, from: jsonData)
let floatValues = o.data.results.flatMap({ $0.winners }).compactMap({ Float($0.prize) })
floatValues.reduce(0, +)
print(floatValues)
} catch let e {
print(e)
}
Step 3: Integrate
We now have the building blocks we need to get this information so let's hook it up to your code by starting with what we want our code to look like.
/// We store our main data type for easy reference
var resultsBySection: [Result]
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView?
{
let header = tableView.dequeueReusableHeaderFooterView(withIdentifier: cellReuseIdentifier) as! OverallHeaderCell
let currentResults = resultsBySection[section]
let prizeTotals = currentResults.flatMap({ $0.winners }).compactMap({ Float($0.prize) })
let totalPriceMoney = prizeTotals.reduce(0, +)
header.textL[0].text = currentResults.name
header.textL[3].text = "\(String(describing: totalPriceMoney))"
return header
}
Notice how in the above code I do not do any JSON decoding in cell dequeueing. Ideally that should be done when we retrieve our JSON and convert it to our types.
Step 4: Refactor
An essential piece of any code experience should contain some reflection into the code we have written and consider how it could be refactored.
In our example above we could probably hardcode the totals onto the controller or create a custom data structure that will do this for us when we parse JSON. Do we always want to manually calculate the totals if we always need this total? We could have a custom function to do the calculation or just do it in our JSON decoding logic.
Anyways, the idea is that we should always look at what we are writing and question how it could be improved

Answer 2

Try this Codable solution to reduce the prizes together:
struct Winners: Codable {
let status: Int
let message: String
let data: DataClass
}
struct DataClass: Codable {
let result: [Result]
let overall: String
}
struct Result: Codable {
let name: String
let response: [Response]
}
class Response: Codable {
let name: String
let prize: Double
init(name: String, prize: Double) {
self.name = name
self.prize = prize
}
enum CodingKeys: String, CodingKey {
case name
case prize
}
enum SerializationError: Error {
case missing(String)
case invalid(String, Any)
}
public required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
name = try container.decode(String.self, forKey: .name)
let prizeString = try container.decode(String.self, forKey: .prize)
guard let prize = Double(prizeString) else {
throw SerializationError.invalid("prize", prizeString)
}
self.prize = prize
}
public func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(name, forKey: .name)
try container.encode("\(prize)", forKey: .prize)
}
}
func testing() {
let winners = try! JSONDecoder().decode(Winners.self, from: jsonData)
let sum = winners.data.result[section].response
.map({ $0.prize })
.reduce(0, +)
print(sum)
}

Answer 3

let sum = winnerArr?[section]["response"].reduce(0, { x, y in
x + y["prize"]
}) ?? 0
As an aside, I would recommend parsing the response and turning it into usable objects rather than dealing with the raw response : https://developer.apple.com/swift/blog/?id=37

Answer 4

Thanks to all of your guys, who helped. I am a newbie and not familiar with Codable. Thanks for introducing me to the same. I will try to understand it and use it for future purposes.
So, coming back to the answer:
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView?
{
self.prizeArr.removeAll()
let header = tableView.dequeueReusableHeaderFooterView(withIdentifier: cellReuseIdentifier) as! OverallHeaderCell
let resArr = self.winnerArr![section]["response"]! as? Array<Dictionary<String,Any>>
for prize in resArr!
{
let doubleStr = prize["prize"] as? NSString
self.prizeArr.append((doubleStr?.doubleValue)!)
}
let sumedArr = prizeArr.reduce(0, +)
let countArr = winnerArr![section]["response"] as? Array<Dictionary<String,Any>>
header.textL[0].text = winnerArr![section]["name"] as? String
header.textL[1].text = "$\(sumedArr)"
header.textL[3].text = "\(String(describing: countArr!.count))"
return header
}
Here I am converting each string to a double and appending it to the prizeArr and then, finally, summing the entire array to get the desired result. But, this is not the ideal way to do it. This answer is for all the newbies like me and please learn Codables.