Is it possible to sort a HashTable?

I have a property that returns a HashTable. I would like to sort it without refactoring my property. Please note: I do not want to return another type. Code:

    /// <summary>
    /// All content containers.
    /// </summary>
    public Hashtable Containers
    {
        get
        {
            Hashtable tbl = new Hashtable();
            foreach (Control ctrl in Form.Controls)
            {
                if (ctrl is PlaceHolder)
                {
                    tbl.Add(ctrl.ID, ctrl);
                }
                // Also check for user controls with content placeholders.
                else if (ctrl is UserControl)
                {
                    foreach (Control ctrl2 in ctrl.Controls)
                    {
                        if (ctrl2 is PlaceHolder)
                        {
                            tbl.Add(ctrl2.ID, ctrl2);
                        }
                    }
                }
            }

            return tbl;
        }
    }

Another option is to construct the hash table as you're already doing, and then simply construct a sorted set from the keys. You can iterate through that sorted key set, fetching the corresponding value from the hash table as needed.

Hashtables work by mapping keys to values. Implicit in this mapping is the concept that the keys aren't sorted or stored in any particular order.

However, you could take a look at SortedDictionary<K,V>.

lubos is right: you can't sort a HashTable. If you could, it wouldn't be a HashTable. You can enumerate the HashTable, and then sort the enumeration. But that would be very slow. Much better to use a SortedDictionary instead.

Sorry, but you can't sort hashtable. You will have to refactor your code to use some sortable collections.

I am quite sure that hash tables cannot be sorted ... ;)

Wikipedia Hash Table

You will need to return something other than a hash table. I won't reiterate what you claim to understand already, but you need to rethink whatever part of your design requires you to return sorted objects in a hash table.

Not exactly a C# answer but I am sure you can make something of it.

In Perl it is common to "sort" a hash table for use in output to the display.

For example:

print "Items: ";
foreach (sort keys %items) {
    print $_, '=', $items{$_}, ' ';
}

The trick here is that Perl doesn't sort the hash, it is sorting a copied list of hash keys. It should be easy enough in C# to extract the hash keys into a list and then sort that list.

There is no point in sorting a hash table because you already have almost constant lookup time. Or at worst O(B) where B is the bucket size.

Of course hash tables can be sorted, but you need to first define what it means to sort a hash table. (Therein lies the issue)

Once you have done that, however, you've invariably removed all the advantages that a hashtable can give you, and you might as well use a sorted array (with binary searching), or use a red-black tree instead.

Noah

I am a new programmer so take everything I say with a grain of salt. But here is what I did when I ran into a similar situation. I created a class that had two variables and then created a List object off those variables and then I used linq to sort those variables.

You can also use DataView to sort the Hashtable. Here is an article that I wrote 5 years ago: http://www.codeproject.com/Articles/37039/Sorting-Hashtable

来源：https://stackoverflow.com/questions/675759/is-it-possible-to-sort-a-hashtable

标签

sorting

hashtable