C# 如何编写iGroup的结果?
我编写了以下LINQ查询:C# 如何编写iGroup的结果?,c#,linq,C#,Linq,我编写了以下LINQ查询: public IEnumerable DailyReturns() { var a = from exec in executions group exec by exec.TimeStamp.Date into execGroup select new { TimeStamp = execGroup.Key, CashFlow = execGroup.Sum(e => e.CashFlow())};
public IEnumerable DailyReturns()
{
var a = from exec in executions
group exec by exec.TimeStamp.Date into execGroup
select new { TimeStamp = execGroup.Key, CashFlow = execGroup.Sum(e => e.CashFlow())};
return a;
}
我收到一个未处理的异常:System.InvalidCastException:指定的强制转换无效。
当我尝试:
foreach (KeyValuePair<DateTime, double> p in s.Executions.DailyReturns())
{
Console.WriteLine(p.Key.ToString() + ',' + p.Value.ToString());
}
您返回的是匿名类型,而不是
KeyValuePair
您可以通过向方法添加适当的类型来解决此问题:
public IEnumerable<KeyValuePair<DateTime,double>> DailyReturns() {
return from exec in executions
group exec by exec.TimeStamp.Date into execGroup
select new KeyValuePair<DateTime,double>(
execGroup.Key
, execGroup.Sum(e => e.CashFlow())
);
}
public IEnumerable DailyReturns(){
从执行中的exec返回
按exec.TimeStamp.Date将exec分组到execGroup中
选择新的KeyValuePair(
execGroup.Key
,execGroup.Sum(e=>e.CashFlow())
);
}
select new{}
生成一个-它不是KeyValuePair
,因此不能强制转换它!
public IEnumerable<KeyValuePair<DateTime,double>> DailyReturns() {
return from exec in executions
group exec by exec.TimeStamp.Date into execGroup
select new KeyValuePair<DateTime,double>(
execGroup.Key
, execGroup.Sum(e => e.CashFlow())
);
}