CorePlot real-time plotting - swift

Question

I was new to swift development. I recently used CorePlot to help me draw the ECG data from sensor in real-time. The sampling rate of sensor is 250 points/sec. At first, I read every 5 points to draw one time then refresh the view till the scatter filled with the view(about 1000 points). But I found that was inefficient and the data would lose.
Afterward I saw that I could insert the update points to change the graph by using -insertDataAtIndex:numberOfRecords. I have referenced to RealTimePlot example in CorePlot, but I don't know how exactly to do it in Swift. Can you give me RealTimePlot example in Swift or tell me how to do it?
Please help me.
typealias plotDataType = [CPTScatterPlotField : Double]
private var scatterGraph : CPTXYGraph? = nil
func plotChart(ecg:[Int]){
let ecgLinePlot = CPTScatterPlot(frame: CGRectZero)
var ecgContentArray = [plotDataType]()
for i in 0 ..< ecg.count { //ecg.count=1000
let y = Double(ecg[i])/65535.0 + 0.05
let x = Double(i) * 0.1
let dataPoint: plotDataType = [.X: x, .Y:y]
ecgContentArray.append(dataPoint)
}
ecgDataForPlot = ecgContentArray
// MARK: - Plot Data Source Methods
func numberOfRecordsForPlot(plot: CPTPlot) -> UInt
{
return UInt(self.ecgDataForPlot.count)
}
func numberForPlot(plot: CPTPlot, field: UInt, recordIndex: UInt) -> AnyObject?
{
let plotField = CPTScatterPlotField(rawValue: Int(field))
if let ecgNum = self.respDataForPlot[Int(recordIndex)][plotField!]{
return ecgNum as NSNumber
}
}

Answer 1

You follow the same process the "Real Time Plot" demo uses. The update action takes place in the -newData: method. The demo calls this method periodically using a timer, but you can supply new data from anywhere, e.g., a callback or delegate from the sensor device.
These are the basic steps to follow:
Remove old points from the beginning of the dataset if adding new ones will make the total dataset larger than what you want to display. Remove them from both the plot and from your local data cache (ecgDataForPlot). You can keep them around if you want the user to be able to scroll back into the history. The demo doesn't need to keep the old data since it scrolls automatically and there is no way to go back and see data from the past.
Update the plot range to include the new data points. The demo animates the change, but this part is optional.
Add the new data points to the local data cache (ecgDataForPlot).
Call -insertDataAtIndex:numberOfRecords: to tell the plot to load the new data. The demo always add new data at the end of the existing dataset which makes sense for a time-series, but you can insert new data anywhere.