Linq GroupBy和多列

Question

class ExpenseClaim 
{ 
    int EmployeeId; 
    int Team; 
    double Cost; 
} 


List<EmployeeExpense> GetEmployeeExpenses() 
{ 
    return _expenseClaims // `_expenseClaims` is `List<ExpenseClaim>` 
      .GroupBy(e => e.EmployeeId) 
      .Select(x => 
       new EmployeeExpense(
         x.Key, 
         // TODO: employee team? 
         x.Sum(e => e.Cost) 
       ); 
} 

請原諒這個頗爲人爲的例子。

如何獲得GetEmployeeExpenses的員工團隊？我假設我需要第二組，但我無法弄清楚語法。

請注意，對於給定的員工，他們的Team將總是相同的，所以我很樂意拿Team，例如按記錄分組的第一個。

所以......

ExpenseClaim { EmployeeId = 1, Team = Sales, Cost = 100 } 
ExpenseClaim { EmployeeId = 1, Team = Sales, Cost = 50 } 

=> 

EmployeeExpense { EmployeeId = 1, Team = Sales, Cost = 150 } 

Answer 1

你的具體情況，你可以使用x.First().Team裏面你選擇，讓您的團隊信息。

對於其他需要在多個字段上進行分組的情況，可以使用匿名類型進行分組。如它

someQuery.GroupBy(f => new { f.Foo, f.Bar }).Select(...);

Answer 2

查詢表達式版本（可能更容易閱讀，這取決於形勢和分組量）：

IEnumerable<EmployeeExpense> GetEmployeeExpenses(List<ExpenseClaim> claims) 
{ 
    return 
     from c in claims 
     group c by c.EmployeeId into groupedById 
     from g in groupedById 
     group g by g.Team into groupedByTeam 
     let firstElement = groupedByTeam.First() 
     select new EmployeeExpense { 
      EmployeeId = firstElement.EmployeeId, 
      Team = firstElement.Team, 
      Cost = groupedByTeam.Sum(e => e.Cost) 
     }; 
}