This example demonstrates how to create a custom group description by deriving from the DataGridGroupDescription class and overriding the GroupNameFromItem method. The custom group description will group items according to the first letter in the value received as a parameter. The example results in the group being present at initial loading; also, when removing and re-adding the group, the custom group description is not triggered. See below for an alternative approach to avoid this. 

The implementation for the custom sort comparer assigned to the group description's SortComparer property is provided below.

VB.NET
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Imports System
Imports System.Collections.Generic
Imports System.Text
Imports Xceed.Wpf.DataGrid
Imports System.Collections
Imports System.Globalization;
Namespace Xceed.Wpf.Documentation
  Public Class AlphabeticalGroupDescription
         Inherits DataGridGroupDescription
    Public Sub New()
      MyBase.New()
    End Sub
    Public Sub New(ByVal propertyName As String)
     MyBase.New(propertyName)
    End Sub
    Public Overrides Function GroupNameFromItem(ByVal item As Object, _
                                                ByVal level As Integer, _
                                                ByVal culture As CultureInfo) As Object
      Dim value As Object = MyBase.GroupNameFromItem(item, level, culture)
      Try
        Dim content As String = Convert.ToString(value)
        value = content.ToUpper().Substring(0, 1)
      Catch e1 As InvalidCastException
      End Try
      Return value
    End Function
  End Class
End Namespace
C#
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using System;
using System.Collections.Generic;
using System.Text;
using Xceed.Wpf.DataGrid;
using System.Collections;
namespace Xceed.Wpf.Documentation
{
  public class AlphabeticalGroupDescription : DataGridGroupDescription
  {
    public AlphabeticalGroupDescription()
      : base()
    {
    }
    public AlphabeticalGroupDescription( string propertyName )
      : base( propertyName )
    {
    }
  
    public override object GroupNameFromItem( object item, int level,
                                              System.Globalization.CultureInfo culture )
    {
      object value = base.GroupNameFromItem( item, level, culture );
      try
      {
        string content = Convert.ToString( value );
        value = content.ToUpper().Substring( 0, 1 );
      }
      catch( InvalidCastException )
      {
      }
      return value;
    }
  }
}

The following code demonstrates how to use the custom group description by adding it to the DataGridCollectionViewSource's GroupDescriptions property.

XAML
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<Grid xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid"
     xmlns:local="clr-namespace:Xceed.Wpf.Documentation">
  <Grid.Resources>     
    <local:ConsonantVowelComparer x:Key="consonantVowelComparer"/>
    <xcdg:DataGridCollectionViewSource x:Key="cvs_orders"
                                       Source="{Binding
                                                Source={x:Static Application.Current},
                                                Path=Orders}">
     <xcdg:DataGridCollectionViewSource.GroupDescriptions>
       <local:AlphabeticalGroupDescription PropertyName="ShipCountry"
                                SortComparer="{StaticResource consonantVowelComparer}"/>
     </xcdg:DataGridCollectionViewSource.GroupDescriptions>
    </xcdg:DataGridCollectionViewSource>
  </Grid.Resources>
  <xcdg:DataGridControl x:Name="OrdersGrid"
                        ItemsSource="{Binding Source={StaticResource cvs_orders}}"/>
</Grid>
VB.NET
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Dim collectionView As New DataGridCollectionView( Orders )
Dim groupDescription As New AlphabeticalGroupDescription( "ShipCountry" )
groupDescription.SortComparer = New ConsonantVowelComparer()
collectionView.GroupDescriptions.Add( groupDescription )
dataGridControl.ItemsSource = collectionView
C#
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DataGridCollectionView collectionView = new DataGridCollectionView( Orders );
AlphabeticalGroupDescription groupDescription = new AlphabeticalGroupDescription( "ShipCountry" );
groupDescription.SortComparer = new ConsonantVowelComparer();
collectionView.GroupDescriptions.Add( groupDescription );
dataGridControl.ItemsSource = collectionView;

The following code provides the implementation for the custom sort comparer that is used to sort, by vowels then consonants, the group descriptions create above.

VB.NET
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Imports System
Imports System.Collections.Generic
Imports System.Text
Imports System.Collections
Namespace Xceed.Wpf.Documentation
  Public Class ConsonantVowelComparer
     Implements IComparer
    Public Sub New()
    End Sub

    Public Function Compare(ByVal x As Object, _
                            ByVal y As Object) As Integer Implements IComparer.Compare
      If (TypeOf x Is String) AndAlso (TypeOf y Is String) Then
        Dim xString As String = x.ToString().ToLowerInvariant()
        Dim yString As String = y.ToString().ToLowerInvariant()
        Dim isXVowel As Boolean = m_vowels.Contains(xString)
        Dim isYVowel As Boolean = m_vowels.Contains(yString)
        If isXVowel Xor isYVowel Then
          If isXVowel Then
            Return -1
          Else
            Return 1
          End If
        End If
        Return String.Compare(xString, yString)
      End If
      Throw New ArgumentException()
    End Function
    Private Const m_vowels As String = "aeiouy"
  End Class
End Namespace
C#
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using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;
namespace Xceed.Wpf.Documentation
{
  public class ConsonantVowelComparer : IComparer
  {
    public ConsonantVowelComparer()
    {
    }
    public int Compare( object x, object y )
    {
      if( ( x is string ) && ( y is string ) )
      {
        string xString = x.ToString().ToLowerInvariant();
        string yString = y.ToString().ToLowerInvariant();
        bool isXVowel = m_vowels.Contains( xString );
        bool isYVowel = m_vowels.Contains( yString );
        if( isXVowel ^ isYVowel )
          return isXVowel ? -1 : 1;
        return String.Compare( xString, yString );      
      }
      throw new ArgumentException();
    }
    private const string m_vowels = "aeiouy";
  }
}

The first example results in the group being present at initial loading; also, when removing and re-adding the group, the custom GroupDescription is not triggered. But by adding the custom GroupDescription directly to the Column, data is not grouped until the end-user drags the column to create the group.

<Window.Resources>
    <local:DateGroupDescription x:Key="myDateGroupDescription"
                                PropertyName="DateTimeFieldName" />
</Window.Resources>

[...]

<xcdg:DataGridControl.Columns>
  <xcdg:Column FieldName="DateTimeFieldName"
              GroupDescription="{StaticResource myDateGroupDescription}" />
</xcdg:DataGridControl.Columns>