Group By using Select statement in Linq

Group By using Select statement in Linq

var query = (from i in SFC.Supplies_ReceiveTrans orderby i.Poprctnm
descending select new { RR = i.Poprctnm });
Result:
RR-01,
RR-01,
RR-02,
RR-02,
RR-02,
RR-TEST,
RR-TEST,
How do i group RR in this kind of statement
Result:
RR-01,
RR-02,
RR-TEST