使用已计算的元素

Question

我发现自己在linq语句中重复计算，我想知道是否可以以某种方式访问已经计算过的元素。这就是我要做的：

var result = testdata.GroupBy(a => new { a.reportinggroup, a.commodity, a.timestep.Year })
                     .Select(g => new EndResult
                            {
                                rundate = rundate.ToShortDateString(),
                                price = g.Sum(a => (a.timestep.ispeak()) ? a.price : 0) / g.Sum(a => (a.timestep.ispeak()) ? 1 : 0),
                                valueposition = g.Sum(a => (a.timestep.ispeak()) ? a.position * a.price : 0) / (g.Sum(a => (a.timestep.ispeak()) ? a.price : 0) / g.Sum(a => (a.timestep.ispeak()) ? 1 : 0)),

                            }).ToList();

效果很好。

这就是我想要做的：

var result = testdata.GroupBy(a => new { a.reportinggroup, a.commodity, a.timestep.Year })
                     .Select(g => new EndResult
                            {
                                rundate = rundate.ToShortDateString(),
                                price = g.Sum(a => (a.timestep.ispeak()) ? a.price : 0) / g.Sum(a => (a.timestep.ispeak()) ? 1 : 0),
                                valueposition = g.Sum(a => (a.timestep.ispeak()) ? a.position * a.price : 0) / price,           
                            }).ToList();

其中价格是我在运行日期之后计算出来的价格。我能以某种方式访问这个吗？

Answer 1

您可以首先选择一个匿名类型来存储此值：

result = testdata.GroupBy(a => new { a.reportinggroup, a.commodity, a.timestep.Year })
.Select(g => new { 
    rundate = rundate.ToShortDateString(), 
    price = g.Sum(a => (a.timestep.ispeak()) ? a.price : 0) / g.Sum(a => (a.timestep.ispeak()) ? 1 : 0),
    group = g
})
.Select(x => new EndResult
{
    rundate = x.rundate,
    price = x.price,
    valueposition = x.group.Sum(a => (a.timestep.ispeak()) ? a.position * x.price : 0) / x.price
}).ToList();

另一种方法是使用“真实”代码：

result = testdata.GroupBy(a => new { a.reportinggroup, a.commodity, a.timestep.Year })
.Select(g => { 
    var price = g.Sum(a => (a.timestep.ispeak()) ? a.price : 0) / g.Sum(a => (a.timestep.ispeak()) ? 1 : 0);
    EndResult endRes = new EndResult { 
        rundate = rundate.ToShortDateString(),
        price = price,
        valueposition = x.group.Sum(a => (a.timestep.ispeak()) ? a.position * price : 0) / price)
    };
    return endRes;
}).ToList();

Answer 2

通过使用查询语法 (from)，您可以使用让子句：

 var result = (from g in  testdata.GroupBy(a => new { a.reportinggroup, a.commodity, a.timestep.Year })
               let price = g.Sum(a => (a.timestep.ispeak()) ? a.price : 0) / g.Sum(a => (a.timestep.ispeak()) ? 1 : 0)
               select new EndResult
               {
                   rundate = rundate.ToShortDateString(),
                   price = price,
                   valueposition = g.Sum(a => (a.timestep.ispeak()) ? a.position * a.price : 0) / price,
                }).ToList();