C# Discussion Boards - CodeProject

Re: update Dictionary with new KeyValuePair set[modified]

27-Mar-10 4:07

Hey all,

I've a dictionary, i sort his keyValuePair set with linq, and now i want to update my dictionary with the sorted set, how can i do that ?

tanks

Dan Mos27-Mar-10 4:35

27-Mar-10 4:35

I don't think you can update the dictionary.

You must create a new one. Something like this:

Dictionary<int, string> original = new Dictionary<int, string>();
            original.Add(2, "absolutely");
            original.Add(1, "undoubtely");

            var sortedKeys = (from rec in original
                             orderby rec.Key
                             select rec.Key).ToList();

            Dictionary<int, string> second = new Dictionary<int, string>();

            for (int i = 0; i < sortedKeys.Count; i++)
            {
                second.Add(sortedKeys[i], original[sortedKeys[i]]);
            }

[Edit]A different option is to use the SortedDictionary [/Edit]

Abhinav S27-Mar-10 4:47

Abhinav S

27-Mar-10 4:47

A dictionary has a Clear method.

Using this method, the Count property is set to 0, and references to other objects from elements of the collection are also released.

Me, I'm dishonest. And a dishonest man you can always trust to be dishonest.
Honestly. It's the honest ones you want to watch out for...

Dan Mos27-Mar-10 5:07

27-Mar-10 5:07

Yeah but then how will he know wich value/object to insert at a given key?

igalep13227-Mar-10 5:07

27-Mar-10 5:07

and if i wont use the Clear method ?
there is no way to add new keyValuePair set to the dictionary ?

Dan Mos27-Mar-10 5:32

27-Mar-10 5:32

My bad. I thought you wanted to sort just on the key and select just the key.

Here's a working solution using the Clear() method.

var sortedKeys = (from rec in original
                              orderby rec.Key ascending, rec.Value ascending                              
                              select rec).ToList();

            //clear the dict
            original.Clear();
            //add the new keyvalue pairs
            for (int i = 0; i < sortedKeys.Count;i++ )
            {
                original.Add(sortedKeys[i].Key, sortedKeys[i].Value);
            }

igalep13227-Mar-10 5:35

27-Mar-10 5:35

guess what,
when original.Clear() is executed, all the sorted set is gone...

Dan Mos27-Mar-10 5:42

27-Mar-10 5:42

Yes and NO.

If you don't use the .ToList() after the Linq then yes.
Else no.

igalep13227-Mar-10 5:45

27-Mar-10 5:45

you right, i forgot the .toList()
tanks...

Daniel Grunwald27-Mar-10 7:18

Daniel Grunwald

27-Mar-10 7:18

Your question does not make sense. A dictionary does not have any defined order.
Yes you can get the pairs out of a dictionary and sort them. But if you insert them in a new/cleared dictionary, there's no guarantee they will keep that order.
The dictionary class is allowed to reorder elements as it sees fit (to make loopup faster). Often the order of insertion is preserved, but it's not guaranteed.
If you need your pairs to stay in sorted order, don't use a dictionary. Either use a List<KeyValuePair<...>>, or (if sorting by key) use a SortedDictionary<...>.