<Grid xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid">
   <Grid.Resources>
      <xcdg:DataGridCollectionViewSource x:Key="cvs_orders"
                                         Source="{Binding Source={x:Static Application.Current}, Path=Orders}">
         <xcdg:DataGridCollectionViewSource.ItemProperties>
            <xcdg:DataGridItemProperty Name="Freight"
                                       GroupSortStatResultPropertyName="AVERAGE_FREIGHT"/>                                        
         </xcdg:DataGridCollectionViewSource.ItemProperties>
         <xcdg:DataGridCollectionViewSource.StatFunctions>
            <xcdg:AverageFunction SourcePropertyName="Freight"
                                  ResultPropertyName="AVERAGE_FREIGHT"/>
         </xcdg:DataGridCollectionViewSource.StatFunctions>
         <xcdg:DataGridCollectionViewSource.GroupDescriptions>
            <xcdg:DataGridGroupDescription PropertyName="EmployeeID"/>
         </xcdg:DataGridCollectionViewSource.GroupDescriptions>
      </xcdg:DataGridCollectionViewSource>
   </Grid.Resources>
   <xcdg:DataGridControl x:Name="OrdersGrid"
                         ItemsSource="{Binding Source={StaticResource cvs_orders}}">
      <xcdg:DataGridControl.Columns>
         <xcdg:Column FieldName="Freight"/>
      </xcdg:DataGridControl.Columns>
      <xcdg:DataGridControl.DefaultGroupConfiguration>
         <xcdg:GroupConfiguration InitiallyExpanded="False">
            <xcdg:GroupConfiguration.Footers>
               <xcdg:GroupHeaderFooterItemTemplate VisibleWhenCollapsed="True">
                  <DataTemplate>
                     <xcdg:StatRow>
                        <xcdg:StatCell FieldName="Freight"
                                       ResultPropertyName="AVERAGE_FREIGHT"
                                       ResultConverterParameter="F2"/>
                     </xcdg:StatRow>
                  </DataTemplate>
               </xcdg:GroupHeaderFooterItemTemplate>
            </xcdg:GroupConfiguration.Footers>
         </xcdg:GroupConfiguration>
      </xcdg:DataGridControl.DefaultGroupConfiguration>
   </xcdg:DataGridControl>
</Grid>