用C＃排序不保存位置

Question

I have a class named move it has a field named val of type int And I have a list of moves named mlist

I wrote this

mlist.Sort((b, a) =>
    {
       if (a.val > b.val)
           return 1;
       else if (a.val == b.val)
           return 0;
       else
           return -1;
    }
    );

at first my list have two objects that both has .val = 0 when I sort the list the place of these two object is changed. But I don't want to this to happen. What can I do?

Answer 1

Sort performs a quicksort which is an unstable sort.

If you want a stable sort you could use the OrderBy method which is available through LinQ

Using OrderBy in your example would be assuming that mList is a List<>

mList = mList.OrderBy(a => a.val).ToList();

Should you desire the reverse ordering, the method is called OrderByDescending

Answer 2

As @Hans Kesting said sorting is unstable. Read about stable sorts here http://www.csharp411.com/c-stable-sort/

Answer 3

You should use orderBy:

   MyComparer comparer=new MyComparer();
   mlist=  mlist.OrderBy(p => p, comparer).ToList();



  public class Comparer : IComparer<YourObject>
    {


        public int Compare(YourObject a, YourObject b)
        {

            if (a.val > b.val)
                return 1;
            else if (a.val == b.val)
                return 0;
            else
                return -1;

        }
    }