iOS Charts Library - How to Handle X-Axis Duplicate Values

Repeating values on x-axis for iOS Charts

it because when you set your chart setup (granurality = 1 and ChartXAxisFormatter) is showing each second in xAxis

I prefer to use array date to show day in axis, with something like this

public class DateValueFormatter: NSObject, IAxisValueFormatter {
    private let dateFormatter = DateFormatter()
    private let dates:[Date]
    
    init(dates: [Date]) {
        self.dates= dates
        super.init()
        dateFormatter.dateFormat = "dd MMM HH:mm"
    }
    
    public func stringForValue(_ value: Double, axis: AxisBase?) -> String {
        if value >= 0 && value < objects.count{
            let date = dates[Int(value)]
            return dateFormatter.string(from: date)
        }   
        return ""
    }
}

if you don't want to change your value formatted you can try to set granularity to 86400 (total seconds in 1 day)

iOS-Charts Library: x-axis labels without backing data not showing

Ok so thanks to @wingzero 's comment, I have been able to get this working. There are a few things required to do so. For simplicity's sake, I am going to explain how to get the "days of the week" labels working as I originally asked. If you follow these steps, however, you should be able to tweak them to format your chart however you like (for example, with months of the year).

1) Make sure that your chart's x-axis minimum and maximum values are set. In this case, you'd want to say: chartView.xAxis.axisMinimum = 0.0 and chartView.axisMaximum = 6.0. This is important for step 2.

2) As Wingzero alluded to, create a subclass of XAxisRenderer that allows us to grab the minimum and maximum values set in step one and determine what values should be passed to our IAxisValueFormatter subclass in step three. In this case:

class XAxisWeekRenderer: XAxisRenderer {

    override func computeAxis(min: Double, max: Double, inverted: Bool) {
        axis?.entries = [0, 1, 2, 3, 4, 5, 6]
    }

}

Make sure to pass this renderer to your chart like this: chartView.xAxisRenderer = XAxisWeekRenderer()

3) Create a subclass of IAxisValueFormatter that takes the values we passed to the chart in step two ([0, 1, 2, 3, 4, 5, 6]) and gets corresponding label names. This is what I did in my original question here. To recap:

public class CustomChartFormatter: NSObject, IAxisValueFormatter {

    var days: = ["S", "M", "T", "W", "T", "F", "S"]

    public func stringForValue(value: Double, axis: AxisBase?) -> String {
        return days[Int(value)]
    }

}

4) Set the labelCount on your graph to be equal to the number of labels you want. In this case, it would be 7. I show how to do this, along with the rest of the steps, below the last step here.

5) Force the labels to be enabled

6) Force granularity on the chart to be enabled and set granularity to 1. From what I understand, setting the granularity to 1 means that if the data your chart passes to stringForValue is not in round numbers, the chart will essentially round said data or treat it like it is rounded. This is important since if you passed in 0.5, it's possible that your stringForValue might not produce the right strings for your labels.

7) Set the value formatter on the xAxis to be the custom formatter you created in step 3.

Steps 4-7 (plus setting the formatter created in step 3) are shown below:

chartView.xAxis.labelCount = 7
chartView.xAxis.forceLabelsEnabled = true
chartView.xAxis.granularityEnabled = true
chartView.xAxis.granularity = 1
chartView.xAxis.valueFormatter = CustomChartFormatter()

How to use String values for X-Axis in Charts instead of doubles?

There's a protocol IAxisValueFormatter that you can implement and achieve your expected result.

EDIT:

How to use it

While initialising

chartView.xAxis.valueFormatter = self

and implementing protocol.

extension LineChart1ViewController: IAxisValueFormatter {
    func stringForValue(_ value: Double, axis: AxisBase?) -> String {
        let months = ["January","February","March","April","May","June","July","Auguest","September","October","November","December"]
        return months[Int(value)]
    }
}

Custom xAxis formatting in iOS Charts library

You need to update your existing code as below.

1. Update your data binding for XAxis:

let chartFormatter = LineChartFormatter(labels: xValues)
let xAxis = XAxis()
xAxis.valueFormatter = chartFormatter
self.xAxis.valueFormatter = xAxis.valueFormatter

2. Update Value Formatter code:

   private class LineChartFormatter: NSObject, IAxisValueFormatter {
   
   var labels: [String] = []
   let dateFormatter = DateFormatter()
   let dateShortFormatter = DateFormatter()
   
   func stringForValue(_ value: Double, axis: AxisBase?) -> String {
   
       if let date = dateFormatter.date(from:labels[Int(value)]) {
           if value == 0 {
               dateShortFormatter.dateFormat = "MMM dd"
               return dateShortFormatter.string(from: date)
           } else {
   
               let prevDate = dateFormatter.date(from:labels[Int(value - 1)])
               dateShortFormatter.dateFormat = "MMM"
               if dateShortFormatter.string(from: date) != dateShortFormatter.string(from: prevDate!) {
                   dateShortFormatter.dateFormat = "MMM dd"
                   return dateShortFormatter.string(from: date)
               } else {
                   dateShortFormatter.dateFormat = "dd"
                   return dateShortFormatter.string(from: date)
               }
           }
       } else {
         return labels[Int(value)]
       }
   }
   
   init(labels: [String]) {
       super.init()
       dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss Z"
       self.labels = labels
   }}
   

By Above code change, you will achieve your Date formatting in XAxis.

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