Sorting Lists with sub items in C#

Question

I'm trying to sort a list of orders and items based on a the earliest (lowest) creation date of one of the items in the list.

So I have:

public MyOrder
{
orderid int;
IList<MyItems> orderitems;
}

public MyItems
{
DateTime itemcreatedate;
}

Say Order1 has two items in it with itemcreatedate 6/1/2010 and 6/15/2010

Order2 has two items in it with itemcreatedate 4/1/2010 and 6/10/2010

I'd like my sorted list to then be Order2, Order1

My meager unfrozen caveman developer brain can see a brute force iterative way to make it happen, but I'm wondering if anyone has a nice clean way.

Answer 1

Try something like this:

List<MyOrder> sortedList = myOrders
    .OrderBy(myOrder => myOrder.OrderItems.Min(myItem => myItem.ItemCreateDate))
    .ToList();

Answer 2

Here is my (untested!) code :

 List<MyOrder> orders = GetSomeOrders();
 var orderCreateDateMap = orders.ToLookup(order => order.orderitems.Min(o2 => o2.itemcreatedate));
 var sortedGroups = orderCreateDateMap.OrderBy(g => g.Key);
 var sortedOrders = sortedGroups.SelectMany(g => g);

The concept is somewhat similar to Mark's one, but I use lookup to avoid IEnumerable<>.Min method to be called multiple times.