LINQ按值对字典排序

Question

I am trying to sort values Descending before pushing them into dictionary. The query works fine but i just need to add sorting functionality.

Following is my original LINQ query

        List<Model> list = query1.Where(x => x.ItemsPrice.Any())
            .GroupBy(x => new { Student = query2.FirstOrDefault(y => y.Id == x. Id).Student.Name })
            .Select(x => new Model
            {
                StudentName = x.Key.Student,
                ClassItems = x.SelectMany(y => y. ItemsPrice)
                              .GroupBy(y => y. Price.item.Name)
                              .ToDictionary(y => y.Key, y => y.Sum(z => z.TotalPrice()))
            }).ToList();

I am trying the following code but it is giving this error

can not implicitly convert IOrderedEnumerables to System.Collection.Generic.Dictioanry.

.ToDictionary(y => y.Key, y => y.Sum(z => z.TotalPrice())).OrderByDescending(y => y.Value)

Answer 1

Something like this should work for you:

public class MyComparer : IComparer<int>
{
  public int Compare(int x, int y)
  {
    return x.CompareTo(y);
  }
}

// ...
private void DoStuff()
{
  var dict = new Dictionary<int, int> {{3, 300}, {2, 200}};
  var sortedDict = new SortedDictionary<int, int>(dict, new MyComparer());
}

Or in your specific scenario:

private class DescendingComparer : IComparer<string>
{
  int IComparer<string>.Compare(string a, string b)
  {              
    return StringComparer.InvariantCulture.Compare(b, a);
  }
}

// ....
ClassItems = new SortedDictionary<string, float>(x.SelectMany(y => y. ItemsPrice)
                                                .GroupBy(y => y. Price.item.Name)
                                                .ToDictionary(y => y.Key, y => y.Sum(z => z.TotalPrice())),
                                               new DescendingComparer());

Note: adjust the key and value type of the sorted dictionary as well as the comparer type according to your needs!

Answer 2

The order that items are stored in a dictionary is not guaranteed. Don't rely on it. When you retrieve items from the dictionary, you can sort it at that point.

"For purposes of enumeration, each item in the dictionary is treated as a KeyValuePair structure representing a value and its key. The order in which the items are returned is undefined."

-- MSDN

As Markus pointed out, if you really need order in your dictionary, use the OrderedDictionary<,> class or the SortedDictionary<,> class .