Linq语句GroupBy的使用

var DetailList = DetailLisAST.GroupBy(a => a.ProjId).Select(a => new
            {
                a.Key
                ,
                Count = a.Count()
            }).ToList();

var DetailList_Num = DetailList_NumAST.GroupBy(a => new { a.ProjTmId, a.SourceType }).Select(a => new
            {
                a.Key
                ,
                Count = a.Count()
            }).ToList();