Question

我的查询如下

var result = from cr in cumulativeresult
    orderby cr.Days
    select new
    {
        Days = cr.Days,
        Com = (from cr1 in cumulativeresult
            where cr1.Days < cr.Days
            group cr1 by 1 into cr1grp
            select
            new
            {
                Count = cr1grp.Count() + cr.Com 
            }),
        ComPercent = Math.Round((double.Parse((
            from cr1 in cumulativeresult
            where cr1.Days < cr.Days
            group cr1 by 1 into cr1grp 
            select cr1grp.Count() + cr.Com).ToString()) / ComCount) * 100, 2)
    };

但是Com和ComPercent并没有作为价值观出现。我如何能够检索其中的值？我检索它们的循环如下

更新

foreach (var item in result)
{
    dt.Rows.Add(item.Days, item.Com, item.ComPercent);
}

我不想对我的foreach循环进行任何处理，我希望我的linq查询中的值。

Answer 1

编译器不知道您的子查询将始终返回一行，因为返回类型仍为IEnumerable（或IQueryable）。这可以通过使用First()或Single()（或相应的..OrDefault()版本）来解决，但是，更常见的是在没有分组的情况下使用Count()，例如：< / p>

Com = (from cr1 in cumulativeresult
       where cr1.Days < cr.Days
       select cr1
      ).Count() + cr.Com,

您可能还想考虑将子查询移动到let子句中，以便可以重复使用它来计算Com和ComPercent：

var result = from cr in cumulativeresult
             let totalCount = 
                      (from cr1 in cumulativeresult
                       where cr1.Days < cr.Days
                       select cr1
                      ).Count() + cr.Com 
             orderby cr.Days
             select new
             {
                Days = cr.Days,
                Com = totalCount,
                ComPercent = Math.Round((double)totalCount / ComCount * 100, 2)
             };

Answer 2

要回答您的问题，您需要选择.First的内容，而不是Linq，知道是1的单个分组。

我也以其他几种方式调整了您的查询：

要获得一些输出，我必须将<更改为<=。
我使用了强制转换而不是重新分析为双倍。

这是整个LinqPad查询：

var cumulativeresult = new[] { new { Days = 0, Com = 0 }, new { Days = 1, Com = 1 } };
var ComCount = cumulativeresult.Count();
var result = from cr in cumulativeresult
             orderby cr.Days
             select new
             {
                 Days = cr.Days,
                 Com = (from cr1 in cumulativeresult
                        where cr1.Days <= cr.Days
                        group cr1 by 1 into cr1grp
                        select
                          new
                          {
                              Count = cr1grp.Count() + cr.Com
                          }
                           ).First().Count,
                 ComPercent = Math.Round((//double.Parse(
                           ((double)(
                           from cr1 in cumulativeresult
                           where cr1.Days <= cr.Days
                           group cr1 by 1 into cr1grp
                           select cr1grp.Count() + cr.Com).First())//.ToString())
                           / ComCount) * 100, 2
                           )
             };

var dt = new DataTable();
dt.Columns.AddRange(new[] {new DataColumn("Days"),new DataColumn("Com"),new DataColumn("ComPercent")  });
foreach (var item in result)
{
    dt.Rows.Add(item.Days, item.Com, item.ComPercent);
}
dt.Dump();

选择Linq中的子查询

2 个答案: