集合中的排序值仅在循环中可见

Question

I have the following code that groups and sorts values within the anonymous collection. When I am in a sorting loop I see that values are correctly sorted. After the loop, they are still in unsorted places ..... why?

class Test
{
    public Guid P1;
    public int P2;
}

var Lista = new List<Test>();

Lista.Add(new Test() { P1 = Guid.Parse("D4651E83-67D6-4BCD-B28D-8173C5AE94F7"), P2 = 2 });
Lista.Add(new Test() { P1 = Guid.Parse("D4651E83-67D6-4BCD-B28D-8173C5AE94F7"), P2 = 1 });

Lista.Add(new Test() { P1 = Guid.Parse("310D74C4-0624-4B1C-9F4E-CB85924CB2B6"), P2 = 4 });
Lista.Add(new Test() { P1 = Guid.Parse("310D74C4-0624-4B1C-9F4E-CB85924CB2B6"), P2 = 3 });

var groups = from g in Lista
                group g.P2 by g.P1 into g
                select new { KeyGroup = g.Key, Rect = g.ToList() };

foreach (var x in groups)
{
    x.Rect.Sort((a, b) => (a.CompareTo(b)));               
}

Answer 1

why?

Because the groups is an enumerable sequence and not a collection. Call ToList() or ToArray() on it before you iterate over it:

var groups = (from g in Lista
              group g.P2 by g.P1 into g
              select new { KeyGroup = g.Key, Rect = g.ToList() }).ToArray();