LINQ-分组依据并从两个不同的对象中选择

Question

I have two lists defined like,

List<First> firstAccount = new List<First>();
List<Second> secondAccount = new List<Second>();

I want to select Account from list firstAccount and Amount always from firstAccount.

var listofFirstAccounts = 
            **(want to select f.Account, s.Begin, s.End,
            sum(f.Amount) as Amount)** -- Don't know how to write this part
            from f in firstAccount
           join s in secondAccount
           on f.Account equals s.Account
           where (
            (f.Begin >= s.Begin && f.Begin <= s.End)
           &&
            (f.End >= s.Begin && f.End <= s.End)
           )
           group f.Account, s.Begin, s.End //Error Here
           select f;

(want to select f.Account, s.Begin, s.End, sum(f.Amount) as Amount) -- Don't know how to write this part

Also getting error at group f.Account, s.Begin, s.End

Answer 1

Something like this should work:

  var result = from account in (from first in firstAccount
                                join second in secondAccount
                                  on first.Account equals second.Account
                                where
                                  ((first.Begin >= second.Begin && first.Begin <= second.Begin) &&
                                   (first.End >= second.Begin && first.End <= second.End)
                                select new
                                {
                                  first.Account,
                                  second.Begin,
                                  second.End,
                                  first.Amount
                                })
               group account by new {account.Account, account.Begin, account.End}
               into groupedAccounts
               select new
               {
                 groupedAccounts.Key.Account,
                 groupedAccounts.Key.Begin,
                 groupedAccounts.Key.End,
                 Sum = groupedAccounts.Sum(a => a.Amount)
               };

Edit: This is by far the ugliest LINQ I have ever written. It should in theory work, assuming that I made the correct assumptions of your data structures. If you don't understand what's going on, I highly recommend that you figure out what's going on. There are plenty of resources explaining various LINQ operations and anonymous types.