how to pass time as xAxis data value in method numberForPlot using core plot? - ios

Question

I need to create graph which is "Heart rate vs time". in xAxis I am showing time which is in format of "HH:mm:ss" and at y Axis its decimal value. My code is as below :
data source for graph:
var graphData:[(String,Double)] = []
let data = ("17:56:35",Double(65))
let data1 = ("18:04:13",Double(95))
let data2 = ("18:8:35",Double(25))
self.graphData.append(data)
self.graphData.append(data1)
self.graphData.append(data2)
Set up graph and plot data code:
func setGraph() {
let tts = CPTMutableTextStyle()
tts.fontSize = 75.0
tts.color = CPTColor(CGColor: UIColor.blackColor().CGColor)
tts.fontName = "HelveticaNeue-Bold"
self.graph.titleTextStyle = tts
self.graph.title = "Heart Rate vs Time"
self.graph.applyTheme(CPTTheme(named:kCPTPlainWhiteTheme))
let plotSpace = graph.defaultPlotSpace as! CPTXYPlotSpace!
plotSpace.allowsUserInteraction = false
let xRange = plotSpace.xRange.mutableCopy() as! CPTMutablePlotRange
xRange.locationDouble = Double(0)
xRange.lengthDouble = Double(1000)
plotSpace.xRange = xRange
let yRange = plotSpace.yRange.mutableCopy() as! CPTMutablePlotRange
yRange.locationDouble = Double(0)
yRange.lengthDouble = Double(210)
plotSpace.yRange = yRange
graph.addPlotSpace(plotSpace)
graph.plotAreaFrame!.paddingTop = 0
graph.plotAreaFrame!.paddingRight = 0
graph.plotAreaFrame!.paddingBottom = graphOffset
graph.plotAreaFrame!.paddingLeft = graphOffset
graph.plotAreaFrame!.masksToBorder = false
// Grid line styles
let majorLineStyle = CPTMutableLineStyle()
majorLineStyle.lineWidth = 0.75
majorLineStyle.lineColor = CPTColor.redColor()
let minorLineStyle = CPTMutableLineStyle()
minorLineStyle.lineWidth = 0.25
minorLineStyle.lineColor = CPTColor.blackColor()
//Axis Line colors
let axisLineStyle = CPTMutableLineStyle()
axisLineStyle.lineWidth = 2.0
axisLineStyle.lineColor = CPTColor.blackColor()
//Axis Label colors
let labelTextStyle = CPTMutableTextStyle()
labelTextStyle.textAlignment = CPTTextAlignment.Left
labelTextStyle.color = CPTColor.blackColor()
//Axis title color
let titleTextStyle = CPTMutableTextStyle()
titleTextStyle.textAlignment = CPTTextAlignment.Left
titleTextStyle.color = CPTColor.blackColor()
titleTextStyle.fontSize = 15
let dataSourceLinePlot = CPTScatterPlot()
let lineStyle = CPTMutableLineStyle()
lineStyle.lineWidth = 3.0
lineStyle.lineColor = CPTColor.blueColor()
dataSourceLinePlot.dataLineStyle = lineStyle
dataSourceLinePlot.identifier = kPlotIdentifier
// dataSourceLinePlot.dataSource = self
let xts = CPTMutableTextStyle()
xts.color = CPTColor(componentRed: 255.0, green: 255.0, blue: 255.0, alpha: 1.0)
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "HH:mm:ss"
let timeformatter = CPTTimeFormatter(dateFormatter: dateFormatter)
timeformatter.referenceDate = NSDate()
let axisSet = graph.axisSet as! CPTXYAxisSet!
let xAxis = axisSet.xAxis as CPTXYAxis!
xAxis.axisTitle = CPTAxisTitle(text: "Elapsed Time", textStyle: xts)
xAxis.labelFormatter = timeformatter
xAxis.majorGridLineStyle = majorLineStyle
xAxis.minorGridLineStyle = minorLineStyle
xAxis.majorIntervalLength = NSNumber(double: 60.0)
let yAxis = axisSet.yAxis as CPTXYAxis!
yAxis.axisTitle = CPTAxisTitle(text: "Heart Rate", textStyle: xts)
let axisFormatter = NSNumberFormatter()
axisFormatter.maximumFractionDigits = 0
axisFormatter.minimumIntegerDigits = 1
yAxis.labelFormatter = axisFormatter
yAxis.titleOffset = 35.0
yAxis.majorIntervalLength = 20
yAxis.majorGridLineStyle = majorLineStyle
yAxis.minorGridLineStyle = minorLineStyle
graph.addPlot(dataSourceLinePlot)
self.IBviewGraph.hostedGraph = self.graph
}
To plot data :
func setGraphData() {
dispatch_sync(dispatch_get_main_queue(), {
let plot = CPTScatterPlot()
plot.dataSource = self
let actualPlotStyle = plot.dataLineStyle!.mutableCopy() as! CPTMutableLineStyle
actualPlotStyle.lineWidth = 2.0
actualPlotStyle.lineColor = CPTColor(CGColor: (UIColor.yellowColor().CGColor))
plot.dataLineStyle = actualPlotStyle
plot.interpolation = .Linear
self.graph.addPlot(plot)
})
}
Data source methods
func numberOfRecordsForPlot(plot: CPTPlot) -> UInt {
return 3
}
func numberForPlot(plot: CPTPlot, field: UInt, recordIndex: UInt) -> AnyObject?{
var num = NSNumber()
let index = Int(recordIndex)
switch field {
case 0://xaxis
return graphData[index].0
case 1://yaxis
return graphData[index].1
default:
break
}
print("coordintes = ",num)
return num
}
My graph is drown but only yAxis points are correct , its not considering xAxis value and so because of that points are at wrong position in graph. I think the value I am passing in method numberForPlot for xAxis is wrong , but don't know how to pass it. Give me some solution.

Answer 1

The x-values in the graphData array are strings. Core Plot expects the datasource to return a numeric value for each index. It's reading the hour from the time string and using that for the x-value.
The x-axis is configured to display numbers in the range 0 to 1,000. Therefore, you need to convert the time data to a number in that range. Keep track of the reference date used to format the axis labels (i.e., store it in an instance variable) and use that to convert the time data to an offset in seconds from the reference date.