C#列表<>按2个值分组

var sums = Orders.GroupBy(x => new { x.CustomerID, x.ProductID })
                 .Select(group => group.Sum(x => x.ProductCount));

我意识到这个线程很旧,但由于我刚刚在语法上遇到了困难,我想我会发布我的其他发现——你可以在一个查询中返回总和和ID(w/o foreach),如下所示:

var sums = Orders
            .GroupBy(x => new { x.CustomerID, x.ProductID })
            .Select(group =>new {group.Key, ProductCount = group.Sum(x => x.ProductCount)});

对我来说,让它发挥作用的棘手之处在于,显然,这笔钱必须混在一起。..

或者,如果你想得到每个总和的ID,你可以这样做

var customerAndProductGroups =
    from order in Orders
    orderby order.CustomerID, order.ProductID // orderby not necessary, but neater
    group order by new { order.CustomerID, order.ProductID };

foreach (var customerAndProductGroup in customerAndProductGroups)
{
    Console.WriteLine("Customer {0} has ordered product {1} for a total count of {2}",
        customerAndProductGroup.Key.CustomerID,
        customerAndProductGroup.Key.ProductID,
        customerAndProductGroup.Sum(item => item.ProductCount));
}

var New1=EmpList。分组依据(z=>z.Age)。OrderBy(员工=>员工主键);

dataGridView1.DataSource=新1;