使用 LINQ 和铸型的订购结果

Question

I am trying to order a list and take the top item. I can't set it to the type I need it to be.

var testFiles = new List<FileProcessing>();
testFiles = GetAll(var1, var2, var3, var3);

result = testFiles.OrderByDescending(item => item.DateRowAdded).Take(1);
return result;

I've got compile time error

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable to 'myType'.

Answer 1

Well, .Take(size) returns a IEnumerable<T> (not single T ) of size at most size . So you can put either

 var array = testFiles
   .OrderByDescending(item => item.DateRowAdded)
   .Take(1)
   .ToArray();

 return array.Length > 0
   ? array[0]
   : SomeCustomDefaultValue; // when testFiles is empty

Or

 return testFiles
   .OrderByDescending(item => item.DateRowAdded)
   .FirstOrDefault(); // when testFiles is empty

Please, note that 2nd version being conciser doesn't allow to provide (in general case) custom default value.

Finally, if testFiles is (very) long and thus sorting ( OrderByDescending ) is slow and memory consuming, you can try Aggregate :

 return testFiles
   .Aggregate((bestSoFar, current) => bestSoFar.DateRowAdded > current.DateRowAdded 
      ? bestSoFar
      : current);