Linq Select Group By

Question

我有以下类结构:

public class PriceLog
{
   public DateTime LogDateTime {get; set;}
   public int Price {get; set;}
}

对于List <PriceLog>,我希望Linq查询生成一个输出,该输出等效于如下所示的数据:

LogDateTime | AVG(价格)
2012年1月| 2000年
2月2012 | 3000

简单地说:我想计算一年中每个月的平均价格.
注意:LogDateTime属性应格式化为LogDateTime.ToString("MMM yyyy")

我尝试了以下内容,但不确定它是否会产生所需的结果:

var result = from priceLog in PriceLogList
                         group priceLog by priceLog.LogDateTime.ToString("MMM yyyy") into dateGroup
                         select new PriceLog { GoldPrice = (int)dateGroup.Average(p => p.GoldPrice), SilverPrice = (int)dateGroup.Average(p => p.SilverPrice)};

Answer 1

这将为您提供一系列匿名对象,包含日期字符串和两个平均价格的属性:

var query = from p in PriceLogList
            group p by p.LogDateTime.ToString("MMM yyyy") into g
            select new { 
               LogDate = g.Key,
               AvgGoldPrice = (int)g.Average(x => x.GoldPrice), 
               AvgSilverPrice = (int)g.Average(x => x.SilverPrice)
            };

如果您需要获取PriceLog对象列表:

var query = from p in PriceLogList
            group p by p.LogDateTime.ToString("MMM yyyy") into g
            select new PriceLog { 
               LogDateTime = DateTime.Parse(g.Key),
               GoldPrice = (int)g.Average(x => x.GoldPrice), 
               SilverPrice = (int)g.Average(x => x.SilverPrice)
            };