将两个lambda表达式中的值相乘

Question

下面的代码将第一个月的容量乘以一个增长因子:

forecastData.Where(c => c.Date == months.ElementAt(1)).Sum(c =>
     (c.Volume * c.Growth))

我也希望能够在这个表达式中使用第6个月的增长值。我可以用x作为第6个月的值所以结果是:

.Sum(c => (c.Volume * c.Growth) * x.Growth)

这可能吗?

数据类:

public class ForecastedVolumeMonthly
{
    public int VolumeMonthlyId { get; set; }
    // Location
    public int DepartureDepoId { get; set; }
    public virtual Depo DepartureDepo { get; set; }
    // Destination
    public int DestinationDepoId { get; set; }
    public virtual Depo DestinationDepo { get; set; }
    // Nationality
    public int NationalityId { get; set; }
    public virtual Country Nationality { get; set; }
    public long? Volume { get; set; }
    public double? Growth { get; set; }
    public DateTime Date { get; set; }
}

Answer 1

没有神奇的Linq语法可以做到这一点，但它非常简单。如果只有一个值，在循环外计算它(Linq Extension):

(注意将months.ElementAt(1)移出循环会更好地提高性能)

DateTime monthParam = months.ElementAt(1);
double? growth = forecastData.Where(x => x.Date.Month == 6)
                                .Select(x => x.Growth).FirstOrDefault();

double? sum = forecastData.Where(c => c.Date == monthParam)
                            .Sum(c =>(c.Volume * c.Growth) * growth);

编辑后注释:

double? sum1 = (from c in forecastData
                where c.Date == monthParam
                let month6Val = forecastData.FirstOrDefault
                                (x => x.DepartureDepo = c.DepartureDepo 
                                    && x.DestinationDepo = c.DestinationDepo)?.Growth
                select c.Volume * c.Growth * month6Val).Sum();