PieGrouping
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Demonstrates the use of stacked pie charts to group pie slices by category.

Stacked pie charts are concentric pies with each successive "point" forming
an inner pie to the previous "point".  Each "point" value contains multiple
pie slices represented by a "series".

This sample creates a stacked pie chart showing the categorization of food
products, with each data entry added to the chart as a separate series.

DataLabels with Compass values of RadialText label each pie element with
series (product) name, value and percentage of the whole.

Grouping of the pie slices is performed by a class of the sample named
PieGrouper.  The PieGrouper class simplifies input of values by
allowing input with a tree like structure, and grouping values along the
branches.  Finally, the class generates ChartDataSeries values for the
chart creating the grouped by category concentric pies.
