C# associative array

Question

I've been using a Hashtable, but by nature, hashtables are not ordered, and I need to keep everything in order as I add them (because I want to pull them out in the same order). Forexample if I do:

pages["date"] = new FreeDateControl("Date:", false, true, false);
pages["plaintiff"] = new FreeTextboxControl("Primary Plaintiff:", true, true, false);
pages["loaned"] = new FreeTextboxControl("Amount Loaned:", true, true, false);
pages["witness"] = new FreeTextboxControl("EKFG Witness:", true, true, false);

And when I do a foreach I want to be able to get it in the order of:

pages["date"]  
pages["plaintiff"]  
pages["loaned"]  
pages["witness"]

How can I do this?

user_91671 · Answer

I believe that .NET has the OrderedDictionary class to deal with this. It is not generic, but it can serve as a decent Hashtable substitute - if you don't care about strict type safety.

I've written a generic wrapper around this class, which I would be willing to share.

http://msdn.microsoft.com/en-us/library/system.collections.specialized.ordereddictionary.aspx

user_22656 · Answer

EDIT: LBushkin is right - OrderedDictionary looks like it does the trick, albeit in a non-generic way. It's funny how many specialized collections there are which don't have generic equivalents :( (It would make sense for Malfist to change the accepted answer to LBushkin's.)

(I thought that...) .NET doesn't have anything built-in to do this.

Basically you'll need to keep a List as well as a Dictionary. When you add to the dictionary, add the key to the list. Then you can iterate through the list and find the keys in insertion order. You'll need to be careful when you remove or replace items though.

user_97890 · Answer

There's no perfect solution before .NET 4.0. In < 3.5 You can:

Use a generic SortedList with integer key-type, and value type of the most-derived common type of your items. Define an integer value (i, let's say) and as you add each item to the SortedList, make the key i++, incrementing it's value as you go. Later, iterate over the GetValueList property of the sorted list. This IList property will yield your objects in the order you put them in, because they will be sorted by the key you used.

This is not lightening-fast, but pretty good, and generic. If you want to also access by key, you need to do something else, but I don't see that in your requirements. If you don't new to retrieve by key, and you add items in key order so the collection doesn't actually have to do its sorting, this is it.

In .NET 4.0 you'll have the generic SortedSet Of T, which will be absolutely perfect for you. No tradeoffs.

user_233028 · Answer

use sorted list i think it will solve your problem becuase SortedList object internally maintains two arrays to store the elements of the list; that is, one array for the keys and another array for the associated values. Each element is a key/value pair that can be accessed as a DictionaryEntry object

SortedList sl = new SortedList();

foreach(DictionaryEntry x in sl) {}

SortedList sl = new SortedList();

foreach(DictionaryEntry x in sl) {}

user_182703 · Answer

Use the KeyedCollection

Its underlying base is a List but provides a dictionary lookup based on key. In this case your key is the strings. So as long as you aren't adding the same key twice you are fine.

http://msdn.microsoft.com/en-us/library/ms132438.aspx

user_229652 · Answer

look at sorted list http://msdn.microsoft.com/en-us/library/system.collections.sortedlist.aspx

user_24315 · Answer

As Haxelit suggests, you might derive from KeyedCollection. It actually uses a List underneath until you hit a certain threshold value, and then it maintains both a List and a Dictionary. If you can use a function to derive one of your keys from one of your values, then this is an easy solution. If not, then it gets pretty messy.

C# associative array

10 Answers