separate 2D array into 2 different arrays in swift

Question

I currently have a 2D Array (from JSON Decoding) that is declared as

struct workoutList : Codable {
  let intervals : [[Double]]
}

init(from decoder: Decoder) throws {
  let values = try decoder.container(keyedBy: CodingKeys.self)
  intervals = try values.decodeIfPresent([[Double]].self, forKey: .intervals)! 
}

When I print out the intervals array, it is a 2D Array that looks like:

Intervals:[[0.0, 50.0], [10.2, 55.0], [10.0, 73.0]]

While I can access the individual values via the matrix eg: intervals[0][1] = 50.0, I think it's easier for my purposes to separate it into 2 diff arrays. (each value in an array set is [time, percentage]. Essentially I'm looking to achieve these results:

[time] = [0.0,10.2,10.0] [percentage] = [50.0, 55.0, 73.0]

I have looked at flatmap but this only results in the removal of the 2D array into 1 single array of the form

[0.0, 50.0, 10.2, 55.0, 10.0 73.0]

I tried to look for examples using map but don't believe it helps.

I finally did this but looks ugly:

let flattenedArray = tabbar.workoutIntervals.flatMap {$0}
  print(flattenedArray) // [0.0, 50.0, 10.2, 55.0, 10.0, 73.0]
  
  var timeArray = [Double]()
  var wattArray = [Double]()
  
  for x in 0...flattenedArray.count - 1 {
    if x % 2 == 0{
      timeArray.append(flattenedArray[x] )
    } else {
      wattArray.append(flattenedArray[x] )
    }
  }
  
  print("time:\(timeArray)") // [ 0.0, 10.2, 10.0]
  print("watt:\(wattArray)") // [50.0, 55.0, 73.0]

Thanks

Joakim Danielson · Accepted Answer · 2020-10-27 08:34:02Z

2

Rather than splitting into 2 arrays you can combine the data in a struct and use map to convert the array

let intervals = [[0.0, 50.0], [10.2, 55.0], [10.0, 73.0]]

struct Interval {
    let time: Double
    let watt: Double
}

let workouts = intervals.map { Interval(time: $0[0], watt: $0[1])}

If you still want them in two arrays I think the easiest is to use forEach

var times = [Double]()
var watts = [Double]()

intervals.forEach {
    times.append($0[0])
    watts.append($0[1])
}

answered Oct 27, 2020 at 8:34

Joakim Danielson

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5 Comments

app4g Over a year ago

when I do a print(workout) I get these which seems odd code[MyProject.VCTrain.(unknown context at $1034aea0c).(unknown context at $1034aea58).Interval(time: 0.0, watt: 50.0), .....]

app4g Over a year ago

To Add-on, I'm using the arrays to do 2 things 1) to draw a line chart where x = time, and y = watt 2) using the time portion of it to do a countdown until when I should switch to the 2nd array sequence

Joakim Danielson Over a year ago

@myjunk That looks more like an issue with how/what you are printing

Joakim Danielson Over a year ago

@myjunk Ok but how is that a problem?

app4g Over a year ago

Thanks! I like the foreach version. Much cleaner. Edit: w/ regard to what I want to achieve. Let's say that lack of experience/knowledge is the problem. Initially I thought I could learn how to do it using the 2D array, but figured this is simpler (to me)

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