<ExtensionAttribute()>
Public Overloads Shared Function GroupBy(Of TSource)( _
   ByVal source As IEntityQuery(Of TSource), _
   ByVal keySelector As IProjectionSelector, _
   ByVal elementSelector As IProjectionSelector _
) As ITypedEntityQuery

Dim source As IEntityQuery(Of TSource)
Dim keySelector As IProjectionSelector
Dim elementSelector As IProjectionSelector
Dim value As ITypedEntityQuery
 
value = EntityQueryExtensions.GroupBy(Of TSource)(source, keySelector, elementSelector)

[ExtensionAttribute()]
public static ITypedEntityQuery GroupBy<TSource>( 
   IEntityQuery<TSource> source,
   IProjectionSelector keySelector,
   IProjectionSelector elementSelector
)

[ExtensionAttribute()]
public:
static ITypedEntityQuery^ GroupBygeneric<typename TSource>
( 
   IEntityQuery<TSource^>^ source,
   IProjectionSelector^ keySelector,
   IProjectionSelector^ elementSelector
) 

var mgr = new DomainModelEntityManager();

var keyPs = new ProjectionSelector("Country");
var elementPs = new ProjectionSelector("CompanyName");

var query = mgr.Customers.GroupBy(keyPs, elementPs);
var results = query.Execute();
var r0List = results.Cast<IGrouping<String, String>>().ToList();