来自数据
OrderID OrderAmt OrderDate
----------- ---------- --------------------
1 10.50 2003-10-11 08:00:00
2 11.50 2003-10-11 10:00:00
3 1.25 2003-10-11 12:00:00
4 100.57 2003-10-12 09:00:00
5 19.99 2003-10-12 11:00:00
6 47.14 2003-10-13 10:00:00
7 10.08 2003-10-13 12:00:00
8 7.50 2003-10-13 19:00:00
9 9.50 2003-10-13 21:00:00
我想显示以下运行总计
OrderId OrderDate OrderAmt Running Total
----------- -------------------- ---------- -------------
1 2003-10-11 08:00:00 10.50 10.50
2 2003-10-11 10:00:00 11.50 22.00
3 2003-10-11 12:00:00 1.25 23.25
4 2003-10-12 09:00:00 100.57 123.82
5 2003-10-12 11:00:00 19.99 143.81
6 2003-10-13 10:00:00 47.14 190.95
7 2003-10-13 12:00:00 10.08 201.03
8 2003-10-13 19:00:00 7.50 208.53
9 2003-10-13 21:00:00 9.50 218.03
从以下列表中
List<OrderData> ord = new List<OrderData>();
ord.Add(new OrderData() { OrderNumber=1, OrderAmount=10.50,
OrderDate=new DateTime(2003,10,11)});
ord.Add(new OrderData() { OrderNumber=2, OrderAmount=11.50,
OrderDate=new DateTime(2003,10,11)});
ord.Add(new OrderData() { OrderNumber=3, OrderAmount=1.25,
OrderDate=new DateTime(2003,10,11)});
ord.Add(new OrderData() { OrderNumber=4, OrderAmount=100.57,
OrderDate =new DateTime(2003,10,12)});
ord.Add(new OrderData() { OrderNumber=5, OrderAmount=19.99,
OrderDate=new DateTime(2003,10,12)});
ord.Add(new OrderData() { OrderNumber=6, OrderAmount=47.14,
OrderDate =new DateTime(2003,10,13)});
ord.Add(new OrderData() { OrderNumber=7, OrderAmount=10.08,
OrderDate=new DateTime(2003,10,13)});
ord.Add(new OrderData() { OrderNumber=8, OrderAmount=7.50,
OrderDate=new DateTime(2003,10,13)});
ord.Add(new OrderData() { OrderNumber=9, OrderAmount=9.50,
OrderDate=new DateTime(2003,10,13)});
如何重塑以下查询
var query = from o in ord
select new
{
OrdNumber=o.OrderNumber,
OrdDate=o.OrderDate,
Amount=o.OrderAmount,
RunntingTotal =ord.Aggregate(0,(o a,o b)=>
{a.OrderAmount+b.OrderAmount;})
};
答案 0 :(得分:5)
您无法使用内置的Aggregate
方法执行此操作。
Darin's answer会为您提供所需内容,但会产生副作用(即查询会在枚举时更新total
变量)。
如果您想要一个没有副作用的“纯粹”查询,那么您需要创建某种Accumulate
扩展方法并使用它而不是Aggregate
:
var query = ord.Accumulate(
new { Order = (OrderData)null, Total = 0.0 },
(a, x) => new { Order = x, Total = a.Total + x.OrderAmount });
foreach (var x in query)
{
Console.WriteLine("{0}\t{1}\t{2}\t{3}",
x.Order.OrderNumber, x.Order.OrderDate, x.Order.OrderAmount, x.Total);
}
// ...
public static class EnumerableExtensions
{
public static IEnumerable<TAccumulate> Accumulate<TSource, TAccumulate>(
this IEnumerable<TSource> source,
TAccumulate seed,
Func<TAccumulate, TSource, TAccumulate> func)
{
if (source == null)
throw new ArgumentNullException("source");
if (func == null)
throw new ArgumentNullException("func");
TAccumulate accumulator = seed;
foreach (TSource item in source)
{
accumulator = func(accumulator, item);
yield return accumulator;
}
}
}
答案 1 :(得分:2)
double total = 0;
var result =
(from o in ord
select new
{
OrdNumber = o.OrderNumber,
OrdDate = o.OrderDate,
Amount = o.OrderAmount,
RunntingTotal = total += o.OrderAmount
}).ToArray();