<ExtensionAttribute()>
Public Overloads Shared Function GroupBy( _
   ByVal source As IQueryable, _
   ByVal keySelector As IProjectionSelector _
) As IQueryable

Dim source As IQueryable
Dim keySelector As IProjectionSelector
Dim value As IQueryable
 
value = QueryableExtensions.GroupBy(source, keySelector)

[ExtensionAttribute()]
public static IQueryable GroupBy( 
   IQueryable source,
   IProjectionSelector keySelector
)

[ExtensionAttribute()]
public:
static IQueryable^ GroupBy( 
   IQueryable^ 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();