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)
                );
}

請原諒相當人為的例子。

如何在GetEmployeeExpenses獲得員工團隊？ 我假設我需要第二組，但我無法解決語法問題。

請注意，對於給定的員工，他們的Team總是會保持一致，所以我很樂意以Team為例，按照記錄分組。

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

在您的特定情況下，您可以在Select中使用x.First().Team來獲取您的團隊信息。

對於實際需要在多個字段上進行分組的其他情況，您可以對匿名類型進行分組。 如

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

Answer 2

查詢它的表達式版本（ 可能更容易閱讀，具體取決於情況和分組數量）：

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)
        };
}