Question

To simplify my question, I’ll will give an example.
Say I have a list of objects containing a datetime and an integer attribute.
I’m ordering my list items first by the datetime field then by the integer attribute.

Item #   Date Value  Int Value
  1      2012-01-01     0
  2      2012-01-01     4
  3      2012-01-01     6
  4      2012-01-01     13

Say I have those 4 items in my list (un-ordered at first, above is how I want it to be in the end).

I’m ordering them simply by:

myList = myList.OrderBy(v=>v.MyDateValue).ThenBy(v=>v.MyIntValue).ToList();

After executing the line above, it ends up like below :

Item #   Date Value  Int Value
  1      2012-01-01     0
  4      2012-01-01     13
  2      2012-01-01     4
  3      2012-01-01     6

At first I thought it interprets my int value as a string perhaps (probably not a logical statement, just been futzing with this for quite some time) then I changed my int values to 10,11,12,13 but the result was still the same.

Any idea why this doesn’t work ? Or what I’m doing wrong?

Answer 1

Solution: change your key selector to v => v.DateValue.Date, if you’re not interested in the time.

I couldn’t duplicate the behavior you described. The following works as expected:

    private class Foo
    {
        public DateTime Date { get; set; }
        public int Id { get; set; }
    }

    static void Main(string[] args)
    {
        var myList = new List<Foo>
                         {
                             new Foo {Date = new DateTime(2012, 01, 01), Id = 12},
                             new Foo {Date = new DateTime(2012, 01, 01), Id = 1},
                             new Foo {Date = new DateTime(2012, 01, 03), Id = 7},
                             new Foo {Date = new DateTime(2012, 01, 01), Id = 4},
                         };

        var newList = myList.OrderBy(v => v.Date).ThenBy(v => v.Id).ToList();
        foreach (var f in newList)
        {
            Console.WriteLine("{0}, {1}", f.Date, f.Id);
        }

        Console.ReadLine();
    }

Output item order is 1, 4, 12, and 7. (7 is last because its date is later.)

I suspect that you have DateTime values whose Time is not 0.

Verify that by changing your key selector to v => v.DateValue.Date.