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Get key by idex from a ordered dictionary

Posted on 2006-10-24
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Last Modified: 2008-01-09
How can I retrieve the key by using the index?

I can retrieve the value by index like: oOrderedDictionary[0].toString()

Is there something similair for a key value?
(I believe a sortedlist has a GetKey() method, but the ordered dictionary does not?)
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Question by:Kai77
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Expert Comment

by:jonorossi
ID: 17795792
Have you tried using the TryGetValue method?
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Author Comment

by:Kai77
ID: 17795845
I am using ASP.net 2.0 and intellisense does not say OrderDictionary has a TryGetValue method
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Expert Comment

by:jonorossi
ID: 17795890
Is there a reason you are using System.Collections.Specialized.OrderedDictionary instead of System.Collections.Generic.Dictionary<TKey,TValue>
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Author Comment

by:Kai77
ID: 17795986
from what i undestand an ordered dictionary the sort order is ordered by the order in which you addes key-value pairs. Does the generic.dictionary do the same?
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Author Comment

by:Kai77
ID: 17796028
I just took a quick look at the Generic.Dictionary .

I believe the TryGetValue needs you to enter a key and will return a value based on that key. What I need is to enter a index and get the key.
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Expert Comment

by:jonorossi
ID: 17796034
If you require that the dictionary be sorted then you should use the generic SortedDictionary:

System.Collections.Generic.SortedDictionary<TKey, TValue>
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Expert Comment

by:jonorossi
ID: 17796213
I see what you are after now. I can't seem to find what you are after in any of the collections built into .NET. For some reason none of them allow you to get the key by an index.
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Accepted Solution

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jonorossi earned 500 total points
ID: 17796543
The reason you can't get the key by index with the SortedDictionary is because it is implemented as a binary tree. However, I am not sure why Microsoft didn't add a method to get the Key by index with the OrderedDictionary. Even the OrderedDictionaryKeyValueCollection which you get by going .Keys doesn't have a method to get out a key.

I was thinking get out the OrderedDictionaryKeyValueCollection from .Keys and enumerate the number of times to get to the index. But the GetEnumerator is declared internal so you can't use a foreach.

The only solution I can see is to build your own dictionary either from scratch or inherited from one of the .NET ones. Or try to get one off the internet. Or if you don't need it to be ordered you'd be able to use one of the .NET collections.

This one by Marc Clifton is pretty good http://www.codeproject.com/csharp/GenericKeyedList.asp
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