使用Linq进行C＃集合操作

Question

I have a collection in this format

IList<ReportRow> MyCollection

Where ReportRow is a

Dictionary<string, object>

So MyCollection might look like this:

    Id1 Id2 Value   Status  Entered
    123 2   56      New     50:01.7
    123 2   76      Old     50:23.0
    123 2   12      New     50:23.0
    127 3   54      Old     50:23.0
    127 3   77      New     59:23.0

...

Is there a way in Linq that I can do this: What I need to do is for each Id1+Id2 combination I need to output the Value where Status is New and where the status is Old. There might be multiple New values for an Id1+Id2 combination so it should pick up the latest New record, using the Entered column to sort.

The new record will contain all the records plus 1 extra column like so:

    Id1 Id2 NewValue    OldValue    Entered
    123 2   12          76          50:23.0
    127 3   77          54          59:23.0

Any help with this would be great

Answer 1

from row in MyCollection
group row by new { row.Id1, row.Id2 } into g
let lastNew = g.OrderByDescending(r => r.Entered)
               .FirstOrDefault(r => r.Status == "New")
let lastOld = g.OrderByDescending(r => r.Entered)
               .FirstOrDefault(r => r.Status == "Old")
select new {
   Id1 = g.Key.Id1,
   Id2 = g.Key.Id2,
   NewValue = (lastNew == null) ? null : (int?)lastNew.Value,
   OldValue = (lastOld == null) ? null : (int?)lastOld.Value,
   Entered = g.OrderByDescending(r => r.Entered).First().Entered
}

Answer 2

This should do it (or be close as this is off the top of my head)

collection.OrderByDescending(r => r.Value.Entered)
          .GroupBy(r => {r.Id1, r.Id2)
          .Select(g => new {
               Id1 = g.Key.Id1,
               Id2 = g.Key.Id2,
               NewValue = g.FirstOrDefault(v => v.Status == "New").Value ?? 0,
               OldValue = g.FirstOrDefault(v => v.Status == "Old").Value ?? 0,
               Entered = g.Last().Entered
           })

If you don't care for the dictionary string key you could do

collection.SelectMany(d => d.Value)
          .OrderByDescending(r => r.Value.Entered)
          .GroupBy(rr => {rr.Value.Id1, rr.Value.Id2)
          .Select(g => new {
               Id1 = g.Key.Id1,
               Id2 = g.Key.Id2,
               NewValue = g.FirstOrDefault(v => v.Status == "New").Value ?? 0,
               OldValue = g.FirstOrDefault(v => v.Status == "Old").Value ?? 0,
               Entered = g.Last().Entered
           })