Linq Select Group By

Question

I have the following class structure :

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

For a List< PriceLog > I want a Linq query to generate an output which is equivalent to the data represented as below:

LogDateTime | AVG(Price)
Jan 2012 | 2000
Feb 2012 | 3000

Simply : I want to compute the average price over each month of the year.
Note: LogDateTime property should be formatted as LogDateTime.ToString("MMM yyyy")

I have tried the following, but not sure whether it will generate the desired result:

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

This will give you sequence of anonymous objects, containing date string and two properties with average price:

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)
            };

If you need to get list of PriceLog objects:

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)
            };

Answer 2

You should try it like this:

var result =
        from priceLog in PriceLogList
        group priceLog by priceLog.LogDateTime.ToString("MMM yyyy") into dateGroup
        select new {
            LogDateTime = dateGroup.Key,
            AvgPrice = dateGroup.Average(priceLog => priceLog.Price)
        };