How to make a grouped BarChart with ios-charts?

Question

I am using ios-charts library.

I would like to group my inverter values so that each year is one group. Unfortunately, the number of monthly values per year may vary.

My data json looks like this:

{"monthlyData":[{"ERTRAG":"30.2989999055862","MONAT":"2","JAHR":"2016"},{"ERTRAG":"154.897000223398","MONAT":"1","JAHR":"2016"},{"ERTRAG":"141.996000155807","MONAT":"12","JAHR":"2015"},{"ERTRAG":"135.449000149965","MONAT":"11","JAHR":"2015"},{"ERTRAG":"319.437000751495","MONAT":"10","JAHR":"2015"},{"ERTRAG":"483.369997739792","MONAT":"9","JAHR":"2015"},{"ERTRAG":"698.112997770309","MONAT":"8","JAHR":"2015"},{"ERTRAG":"771.764000892639","MONAT":"7","JAHR":"2015"},{"ERTRAG":"736.611003398895","MONAT":"6","JAHR":"2015"},{"ERTRAG":"737.237999916077","MONAT":"5","JAHR":"2015"},{"ERTRAG":"720.181995391846","MONAT":"4","JAHR":"2015"},{"ERTRAG":"484.979001283646","MONAT":"3","JAHR":"2015"},{"ERTRAG":"249.974001646042","MONAT":"2","JAHR":"2015"},{"ERTRAG":"92.8830004036427","MONAT":"1","JAHR":"2015"},{"ERTRAG":"52.7970000207424","MONAT":"12","JAHR":"2014"},{"ERTRAG":"181.025999426842","MONAT":"11","JAHR":"2014"},{"ERTRAG":"332.789002537727","MONAT":"10","JAHR":"2014"},{"ERTRAG":"482.244999885559","MONAT":"9","JAHR":"2014"},{"ERTRAG":"602.811999320984","MONAT":"8","JAHR":"2014"},{"ERTRAG":"699.872003316879","MONAT":"7","JAHR":"2014"},{"ERTRAG":"828.212007522583","MONAT":"6","JAHR":"2014"},{"ERTRAG":"679.010004997253","MONAT":"5","JAHR":"2014"},{"ERTRAG":"635.115998744965","MONAT":"4","JAHR":"2014"},{"ERTRAG":"559.617002010345","MONAT":"3","JAHR":"2014"},{"ERTRAG":"265.135001063347","MONAT":"2","JAHR":"2014"},{"ERTRAG":"165.272998273373","MONAT":"1","JAHR":"2014"},{"ERTRAG":"134.578999936581","MONAT":"12","JAHR":"2013"},{"ERTRAG":"153.774000287056","MONAT":"11","JAHR":"2013"},{"ERTRAG":"321.733997344971","MONAT":"10","JAHR":"2013"},{"ERTRAG":"482.768000483513","MONAT":"9","JAHR":"2013"},{"ERTRAG":"692.864000797272","MONAT":"8","JAHR":"2013"},{"ERTRAG":"846.429007053375","MONAT":"7","JAHR":"2013"},{"ERTRAG":"709.758005619049","MONAT":"6","JAHR":"2013"},{"ERTRAG":"532.493996858597","MONAT":"5","JAHR":"2013"},{"ERTRAG":"462.539998054504","MONAT":"4","JAHR":"2013"},{"ERTRAG":"419.105004012585","MONAT":"3","JAHR":"2013"},{"ERTRAG":"143.189998820424","MONAT":"2","JAHR":"2013"},{"ERTRAG":"78.720000628382","MONAT":"1","JAHR":"2013"},{"ERTRAG":"90.1430006623268","MONAT":"12","JAHR":"2012"},{"ERTRAG":"155.483000457287","MONAT":"11","JAHR":"2012"},{"ERTRAG":"348.231998205185","MONAT":"10","JAHR":"2012"},{"ERTRAG":"598.037001848221","MONAT":"9","JAHR":"2012"},{"ERTRAG":"729.740003108978","MONAT":"8","JAHR":"2012"},{"ERTRAG":"676.923998832703","MONAT":"7","JAHR":"2012"},{"ERTRAG":"694.879002094269","MONAT":"6","JAHR":"2012"},{"ERTRAG":"811.281997680664","MONAT":"5","JAHR":"2012"},{"ERTRAG":"489.765002369881","MONAT":"4","JAHR":"2012"},{"ERTRAG":"538.866001605988","MONAT":"3","JAHR":"2012"},{"ERTRAG":"277.856996208429","MONAT":"2","JAHR":"2012"},{"ERTRAG":"155.854999214411","MONAT":"1","JAHR":"2012"},{"ERTRAG":"148.157999750227","MONAT":"12","JAHR":"2011"},{"ERTRAG":"230.409998774529","MONAT":"11","JAHR":"2011"}]}

I tried the following:

var months = Array<String>()
var years = Array<String>()
var dataEntries: [BarChartDataEntry] = []
var dataSets: [BarChartDataSet] = []
var overallSum = 0.0
var year = 2010 //monthlyValues[0].year
var count = 0
var chartDataSet: BarChartDataSet?

for i in 0..<monthlyValues.count {
  // if year is different, create new barchartdataset
  if monthlyValues[i].year != year {
    years.append("\(monthlyValues[i].year)")
    chartDataSet = BarChartDataSet(yVals: dataEntries, label: "\(year)")
    chartDataSet!.colors = [UIColor.whiteColor()]
    dataSets.append(chartDataSet!)
    year = monthlyValues[i].year
    dataEntries = []
    //months = []
    count = 0
  }
  months.append("\(monthlyValues[i].month)")
  overallSum += monthlyValues[i].amount

  let dataEntry = BarChartDataEntry(value: monthlyValues[i].amount, xIndex: count)
  count++
  dataEntries.append(dataEntry)
}
let chartData = BarChartData(xVals: months, dataSets: dataSets)
self.barChartView.data = chartData

This results in five series with the right year labels in the legend but there is no group separator in the chart and also the number of bars per year is either 4 or 5 (expected = 12).

Thanks for any hint on this!

Answer 1

You got something wrong here. Right now you are creating a new DataSet for every year.

What you need to do is create as many DataSets as you want bars per group where one DataSet represents one bar in each group. (e.g. DataSet 1 represents every first bar of a group, DataSet 2 every second bar of a group, ...)

As an example, imagine a chart like this with 4 groups of 3 bars per group. Each group represents one year.

||| ||| ||| |||

• The setup shown above requires 3 DataSets (one for each group)
• Entries in the same group have the same x-index (e.g. in the first group all have x-index 0)
• It consists of a total of 12 entries
• Each DataSet contains 4 entries with Entry x-indices ranging from 0 to 3

Here you can find an example of the scenario described above and check out the documentation.