' Creates a Hashtable object with one entry for each unique
' subitem value (or initial letter for the parent item)
' in the specified column.
Private Function CreateGroupsTable(column As Integer) As Hashtable
    ' Create a Hashtable object.
    Dim groups As New Hashtable()
    
    ' Iterate through the items in myListView.
    Dim item As ListViewItem
    For Each item In myListView.Items
        ' Retrieve the text value for the column.
        Dim subItemText As String = item.SubItems(column).Text
        
        ' Use the initial letter instead if it is the first column.
        If column = 0 Then
            subItemText = subItemText.Substring(0, 1)
        End If 

        ' If the groups table does not already contain a group
        ' for the subItemText value, add a new group using the 
        ' subItemText value for the group header and Hashtable key.
        If Not groups.Contains(subItemText) Then
            groups.Add( subItemText, New ListViewGroup(subItemText, _
                HorizontalAlignment.Left) )
        End If
    Next item
    
    ' Return the Hashtable object.
    Return groups
End Function 'CreateGroupsTable