linq对datatable group分组并求和

查询出来的表dtSumNaturalWorkHour，根据PersonName，ProjectName对WorkHour求和。

var query = dtSumNaturalWorkHour.AsEnumerable().GroupBy(d => new { PersonName = d.Field<string>("PersonName"), ProjectName = d.Field<string>("ProjectName")  
                   })  
              .Select(g => new  
              {  
                  PersonName = g.Key.PersonName,  
                  ProjectName = g.Key.ProjectName,  
                  num = g.Sum(d => Convert.ToDouble(d["WorkHour"])),  
              });  

 只根据一列值group 的查询求和:根据PersonName对WorkHour求和.

var dt=  dtSumNaturalWorkHour.Rows.Cast<DataRow>().GroupBy<DataRow, string>(row => Convert.ToString(row["PersonName"])).  
                   Select(group => new { group.Key, Value = group.Sum(x => Convert.ToDouble(x["WorkHour"])) });