Sort a Hashset .Net 3.5

问题:

How can one sort a HashSet<string> in c# .Net 3.5 ?

回答1:

You don't. By definition, a HashSet is not sorted.

If you want a sorted hash set, then you should use a SortedSet. The methods it exposes are essentially a superset of those provided by HashSet, including the ability to sort its contents.

回答2:

You can use the OrderBy method, either an IComparer (i.e. http://msdn.microsoft.com/en-us/library/bb549422.aspx ) or using your comparer inline with some lambdas (i usually use predicates for my comparisons as per below).

See as per link:

        class Pet
        {
            public string Name { get; set; }
            public int Age { get; set; }
        }

        public static void OrderByEx1()
        {
            Pet[] pets = { new Pet { Name="Barley", Age=8 },
                           new Pet { Name="Boots", Age=4 },
                           new Pet { Name="Whiskers", Age=1 } };

            IEnumerable<Pet> query = pets.OrderBy(pet => pet.Age);

            foreach (Pet pet in query)
            {
                Console.WriteLine("{0} - {1}", pet.Name, pet.Age);
            }
        }

        /*
         This code produces the following output:

         Whiskers - 1
         Boots - 4
         Barley - 8
        */

Read more: http://msdn.microsoft.com/en-us/library/bb534966.aspx

回答3:

HashSet<string> is not sorted by design. If you want to sort the items once (~not often) then you can use OrderBy LINQ method (because HashSet<string> implements IEnumerable<string>): hs.OrderBy(s => s);

If you need sorted hashset then you can use SortedDictionary class - just use some dummy type (i.e. bool) for TValue generic parameter.

The SortedSet class is not available in .NET 3.5.