如何在求和另一个的同时汇总一个属性？

Question

我有一张发票清单，每条记录都包含一个客户 ID 和一个金额。目的是生成一个付款列表，其中每个客户的每笔付款都是唯一的（每个客户可能有多张发票）并将相关发票的金额相加。

生成不同发票的列表（关于客户 ID）是 very easy。问题是我只有第一张发票金额的价值，而不是总和。

List<Payment> distinct = invoices
  .GroupBy(invoice => invoice.CustomerId)
  .Select(group => group.First())
  .Select(invoice => new Payment
  {
    CustomerId = invoice.CustomerId,
    Total = invoice.Amount
  }).ToList();

是否有流畅的 LINQ-fu 或我需要在我的列表中使用 foreach？

Answer 1

如果你有这样的东西

Invoice[] invoices = new Invoice[3];

invoices[0] = new Invoice { Id = 1, Amount = 100 }; 
invoices[1] = new Invoice { Id = 1, Amount = 150 }; 
invoices[2] = new Invoice { Id = 2, Amount = 300 };

那么你的目标可以是

var results = from i in invoices
              group i by i.Id into g
              select new { Id = g.Key, TotalAmount = g.Sum(i => i.Amount)};

Answer 2

根据jmelosegui的回答：

List<Payment> distinct = invoices
   .GroupBy(c => c.CustomerId)
   .Select(c => new Payment
   {
     CustomerId = c.Key, 
     Total = c.Sum(x => x.Amount)
   }).ToList();

如何在求和另一个的同时汇总一个属性？

How to aggregate over one property while summing another?

c#

linq

aggregate

如何在求和另一个的同时汇总一个 属性？

How to aggregate over one property while summing another?

c#

linq

aggregate

如何在求和另一个的同时汇总一个属性？