How to keep a Dictionary ordered?

Question

I have a Dictionary<string, Func<string, string>>. I use the keys to provide the items of a drop-down which allows the user to select which algorithm to run. Then I can conveniently feed the selected value back into the dictionary to get the relevant function.

// Initialization
my_dict["Function #1"] = func1;
my_dict["Function #2"] = func2;

...

// Executing
result = my_dict[user_choice](input);

Now, when populating the drop down (a System.Windows.Forms.ComboBox) I loop through the keys of this with foreach. MSDN warns that System.Collections.Generic.Dictionary is not guaranteed to have a stable order. But in practice I know that the order is pretty stable, so it works for now. I do want the functions to be ordered nicely for the user.

However, I want to do this correctly - ie. by using a data structure that guarantees order stability. Unfortunately OrderedDictionary is not helpful, since it forces the values to be objects; I'd like to keep them function delegates. At the same time, I don't want to add too much needless complexity (for instance, I could store a copy of the keys as a List<string> to use for order, but that seems like a poor solution).

What can I do?

Note: Looks like some people assumed that I want my items to be in alphabetical order. I don't. I want them to stay in the same order that I added them in. That is, if key Function #2 is added before Function #1, it will come before it in the order.

Can you please clarify why basic sorted `List>>` does not work? (assuming your "drop-downs" support selected value/index along with selected text)... — Alexei Levenkov, Jun 18 '15 at 05:26
In case you plan to use SortedDictionary, then till the point your key is string its fine, else you need a IEqualityComparer for TKey, check this link - http://stackoverflow.com/questions/2705607/sorting-a-dictionary-in-place-with-respect-to-keys — Mrinal Kamboj, Jun 18 '15 at 06:33
@AlexeiLevenkov you should post your solution as an answer because the other two answers are not answers to this question. — user829755, Jun 06 '19 at 08:28
Use non-generic OrderedDictionary or implement it yourself as in this older question: https://stackoverflow.com/questions/2629027/no-generic-implementation-of-ordereddictionary/64214691?noredirect=1#comment113553608_64214691 — mireazma, Oct 06 '20 at 09:21

ckruczek · Answer 1 · 2015-06-18T07:00:05.377

6

Instead of using the OrderedDictionary, you should use the SortedDictionary<TKey, TValue>.

This one is sorted by the key. So for your example by your Strings. This should suffice.

Update:

If you are not using any native comparable type you need to implement the IEqualityComparer<T> interface for your key-class.

edited Jun 18 '15 at 07:00

answered Jun 18 '15 at 05:24

ckruczek

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For TKey you still may need IEqualityComparer, assuming key is not String – Mrinal Kamboj Jun 18 '15 at 06:34
@MrinalKamboj: Yep and where is the problem, though? I think he is able to implement a proper one. – ckruczek Jun 18 '15 at 06:36
Issue is you need to define that as part of your solution, else its incomplete, and will work only because OP is using string key – Mrinal Kamboj Jun 18 '15 at 06:36
1

@MrinalKamboj: Its definitly not an issue of my answer. I am not the teacher for the complete programming language. He should be able to do some work for his own. – ckruczek Jun 18 '15 at 06:38
Alright if you are not willing to learn or accept, I can do little. Answer should be as complete as possible. – Mrinal Kamboj Jun 18 '15 at 06:39
Hahaha...do whatever makes you happy. So should I also explain how to initialize and how to add the content to the dictionary...come on. Thats so childish right now. – ckruczek Jun 18 '15 at 06:42
Sooo...are you more happy with this answer? – ckruczek Jun 18 '15 at 06:46
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But I don't want them in alphabetical order. I already have my own order. – Superbest Jun 18 '15 at 09:52
2

Then implement the Comparer with your prefered order. – ckruczek Jun 18 '15 at 09:57
This is NOT the answer. The OP does not want to sort at all by any of the key or values, but only the order they were added to the colleciton. – John Stock Nov 18 '21 at 09:42

score -3 · Answer 2 · answered Jun 18 '15 at 05:52

-3

You can also use lambda expression to sort dictionary by Key or by Value like this.

 Dictionary<int, string> myDic = new Dictionary<int, string>();
                myDic.Add(1, "a");
                myDic.Add(2, "b");
                myDic.Add(3, "c");
                myDic.Add(4, "d");
                myDic.Add(5, "e");
                myDic.OrderBy(cond => cond.Key); //sort by key
                myDic.OrderBy(cond => cond.Value); //sort by value

answered Jun 18 '15 at 05:52

Dev D

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This will fail, it's incorrect , check this link - http://stackoverflow.com/questions/8110324/how-to-sort-a-dictionary-by-key – Mrinal Kamboj Jun 18 '15 at 06:36
OP does not want to sort by key or value, but they order they were added to the collection – John Stock Nov 18 '21 at 09:43

How to keep a Dictionary ordered?

2 Answers2

Update:

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