How to calculate Stochastic Oscillator in Swift

To calculate the stochastic oscillator (STOCH) in Swift, you would need to follow these steps:

1. Obtain the historical data for the security you are analyzing. This data should include the closing prices and high and low prices for each period (e.g. daily, weekly, etc.).
2. Calculate the %K line by applying the formula:
   %K = (Current Close - Lowest Low) / (Highest High - Lowest Low) * 100
3. Calculate the %D line by taking the average of %K over a certain number of periods, usually 14 periods.
4. Finally, you can plot the %K and %D lines on a chart to visualize the data.

The code can be something like this:

func calculateSTOCH(closingPrices: [Double], highPrices: [Double], lowPrices: [Double]) -> ([Double], [Double]) {
    var kLine: [Double] = []
    var dLine: [Double] = []
    
    for i in 0..<closingPrices.count {
        let low = lowPrices[max(0, i-14)..<i+1].min()!
        let high = highPrices[max(0, i-14)..<i+1].max()!
        let k = (closingPrices[i] - low) / (high - low) * 100
        kLine.append(k)
    }
    
    for i in 3..<closingPrices.count {
        let d = kLine[(i-3)..<i].reduce(0, +) / 3
        dLine.append(d)
    }
    
    return (kLine, dLine)
}

Please note this is a sample code and it could be different based on your data structure and the way you handle it but it should give you a good idea on how to start. Also, the period of 14 is a standard but you can adjust it to your needs.