Question

public class Product {
    public List<DateTime> FailureDates { get; set; }
}

I have a List<Product> and then I’m trying to do a grouping based on a List<DateTime> for use in a chart. The grouping is supposed to be based on the Year of the DateTime object. So I would want the end result to look something like:

Total Failures by Year

2012: 1,

2011: 5,

2010: 3

… and so on.

I originally had this working before the DateTime object became a list with the following code:

return Json.Encode(Products.Where(s => s.FailureDate != DateTime.MinValue).GroupBy(s => s.FailureDate.Year).Select(s => new { Year = s.Key.ToString(), FailureCount = s.Count() }).ToArray());

But, now that DateTime is a List so I’m not sure how to go about grouping it. I am thinking a merge needs to occur for this to work, so maybe the LINQ code will just end up being too messy and I would be better of using a non-LINQ solution (e.g. iterating through my products and then iterating through my dates and building out a dictionary to keep track of the counts).

Answer 1

This would work for you.

var query = from p in Products
            from f in p.FailureDates 
            where f != DateTime.MinValue
            group f by f.Year into g
            select new
            {
              Year = g.Key.ToString(),
              FailureCount = g.Count(),
            }

Or to use your example, just add a SelectMany on Products like this

return Json.Encode(Products.SelectMany(p => p.FailureDates)
                           .Where(s => s != DateTime.MinValue)
                           .GroupBy(s => s.Year)
                           .Select(s => new { Year = s.Key.ToString(), FailureCount = s.Count() }).ToArray());