Question

I have some data in a List of User defined types that contains the following data:

name, study, group, result, date. Now I want to obtain the name, study and group and then a calculation based onthe result and date. The calculation is effectively:

log(result).where max(date) minus log(result).where min(date)

There are only two dates for each name/study/group, so the result from the maximum data (log) minus the result from the minumum date (log). here is what I have tried so far with no luck:

 var result = 
    from results in sortedData.AsEnumerable()
    group results by results.animal
    into grp
    select new
    {
         animal = results.animal,
         study = results.study,
         groupNumber = results.groupNumber,
         TGI = System.Math.Log(grp.Select(c => c.volume)
                                  .Where(grp.Max(c=>c.operationDate)))
             - System.Math.Log(grp.Select(c => c.volume)
                                  .Where(grp.Min(c => c.operationDate)))
    };

Anybody any pointers? Thanks.

Answer 1

It isn’t entirely clear how the grouping relates to your problem (what sense does it make to extract a property from a range variable after it has been grouped?), but the part you’re having difficult with can be solved easily with MaxBy and MinBy operators, such as the ones that come with morelinq.

var result = from results in sortedData.AsEnumerable()
             group results by results.animal into grp
             select new
             {
                animal = grp.Key,
                study = ??,
                groupNumber = ??,
                TGI  =  Math.Log(grp.MaxBy(c => c.operationDate).volume) 
                      - Math.Log(grp.MinBy(c => c.operationDate).volume)    
              };

Otherwise, you can simulate these operators with Aggregate, or if you don’t mind the inefficiency of sorting:

var result = from results in sortedData.AsEnumerable()
             group results by results.animal into grp

             let sortedGrp = grp.OrderBy(c => c.operationDate)
                                .ToList()
             select new
             {
                animal = grp.Key,
                study = ??,
                groupNumber = ??,
                TGI  = sortedGrp.Last().volume  - sortedGrp.First().volume               
             };