I think that the easiest way to go here is to simply order the data prior to feeding the chart. Once you have the data sorted so that Europe appears before North America, and Asia appears last, the grouping should automatically make Europe as the first group and North America as the second. Alternatively, I suppose that you can use custom sort descriptors which require a bit more work.
On a side note I would like to mention that you are using the old RadChart, which has many limitations and it is in maintenance mode now. We suggest you use the new RadChartView for new development. The chartview is actually a set of controls, such as the RadCartesianChart, RadPieChart, RadPolarChart, ChartDataSource. The chartview does not have any built-in grouping or sorting capabilities, and if you need grouping or sorting, you need to do it before you set the ItemsSource. However, it really results in the same amount of work as setting up the group/sort descriptors in the old chart.
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