How can I get the data I need out of this array of arrays?

Question

I need to parse JSON from an API to get two arrays of data, one for Times, and one for Prices.

Here is the request:

func getReq(arr: Bool, completion: @escaping (Bool) -> ()){
    Dates.shared.formatDate()

    switch graphSetup {
    case .day:
        days = "1"
    case .week:
        days = "14"
    }

    let url = "https://api.coingecko.com/api/v3/coins/bitcoin/market_chart?vs_currency=usd&days=1"

    Alamofire.request(url).responseJSON { response in
        switch response.result {
        case .failure(let error):
            // Do whatever here
            return

        case .success(let data):
            // First make sure you got back a dictionary if that's what you expect
            let responseJSON = JSON(response.result.value!)
            if responseJSON.count != 0 {

                //do whatever you want with your object json

                parse(json: responseJSON)
                print(responseJSON)
                let gd = responseJSON["prices"].arrayValue

                completion(arr)
            }
        }
    }

This is exactly what JSON returns (print(responseJSON) I shortened it.

let json = "{
  "prices" : [
[
  1535841336422,
  7186.4600704446984
],
[
  1535841628453,
  7187.2085293179398
],
[
  1535841936398,
  7189.7057414152769
],
... many others ...,
[
  1535889024161,
  7210.4807839639352
],
[
  1535889339150,
  7211.0670314913395
 ]
]
}"

After parsing, I get this array of arrays. How can I separate the times from the prices while keeping them in the correct order so that I can create a chart with [Times] as the x-axis and [Prices] as the y?

I am thinking something like this:

var times: [Int] = [] // Will probably convert to traditional date for chart
var prices: [Double] = []

So I end up with:

print(times)
[1535837138223,1535837424517,1535837741575,...]
print(prices)
[5560.902754859002,5542.734892949798,5539.4334214537,...]

and can now set up my chart correctly. How can I do this? Alternatively, if there is a better way to set up my chart data, (I am using danielgindi/Charts for iOS) please let me know.

@LeoDabus sorry, the first part of code in the question is what is returned from the server. I will edit and add in full any other details it returns — Peter Ruppert
– Peter Ruppert, Commented Sep 2, 2018 at 22:03
@LeoDabus edited to what console shows when printing the response. If someone can give the reason for the downvote so that I can improve, thank you. — Peter Ruppert
– Peter Ruppert, Commented Sep 2, 2018 at 22:43

Leo Dabus · Accepted Answer · 2018-09-03 20:37:18Z

1

You need to structure your data and create a custom encoder/decoder to encode/decode your array of different data types UInt64 (epoch unix time) and Double (price):

struct Root: Codable {
    let prices: [Price]
}
struct Price: Codable {
    let date: Date
    let price: Double
}

extension Price {
    public init(from decoder: Decoder) throws {
        var unkeyedContainer = try decoder.unkeyedContainer()
        let date = try unkeyedContainer.decode(UInt64.self).date
        let price = try unkeyedContainer.decode(Double.self)
        self.init(date: date, price: price)
    }
    public func encode(to encoder: Encoder) throws {
        var unkeyedContainer = encoder.unkeyedContainer()
        try unkeyedContainer.encode(date.unixEpochTime)
        try unkeyedContainer.encode(price)
    }
}

extension UInt64 {
    var date: Date {
        return Date(timeIntervalSince1970: TimeInterval(self)/1000)
    }
}
extension Date {
    var unixEpochTime: UInt64 {
        return UInt64(timeIntervalSince1970*1000)
    }
}

Playground testing:

let json = """
{"prices": [[1535837138223,5560.902754859002],
            [1535837424517,5542.734892949798],
            [1535837741575,5539.4334214537]]}
"""

do {
    let prices = try JSONDecoder().decode(Root.self, from: Data(json.utf8)).prices
    print(prices.first!.date.description(with:.current))  // "Saturday, September 1, 2018 at 6:25:38 PM Brasilia Standard Time\n"
    print(prices.first!.price)  // "5560.902754859\n"

} catch {
    print(error)
}

edited Sep 3, 2018 at 20:37

answered Sep 2, 2018 at 22:39

Leo Dabus

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4 Comments

Peter Ruppert Over a year ago

very helpful thank you. I think I understand what is going on, just to be clear here try JSONDecoder().decode(Root.self, from: Data(json.utf8)), i will put my responseJSON like: try JSONDecoder().decode(Root.self, from: Data(responseJSON.utf8)) correct? I will try it the morning and let you know.

Leo Dabus Over a year ago

Just replace Data(json.utf8) with the data response response.data from your alamofire request inside your success case.

Peter Ruppert Over a year ago

Works perfectly, I am just now trying to figure out how to get all of the values and add to a new array, as I can only access them individually. How would I print all prices in the prices struct for example, or append an array with all values in prices.price, as I can only access prices.first!.price or prices.last!.price.

Peter Ruppert Over a year ago

I've got it, 'for element in prices { print(element.price) }'

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