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

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

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

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

var mgr = new DomainModelEntityManager();
var entityType = typeof(Customer);
var rootQuery = EntityQuery.Create(entityType);
var ps = new ProjectionSelector("Country");

var query = rootQuery.GroupBy(ps);
var results = query.Execute();