Hello,

I'm having trouble using Dictionary classe. I want to use a Dictionary as a
key for another Dictionary. The following code gives a sample of what I'm
talking about.

Dictionary myDates = new Dictionary<Dictionary<string, string>, DateTime>();

The 'Add' or 'ContainsKey' methods need a Dictionary<string, string> as a
(first) parameter, but how to pass this kind of parameter without
instanciating another Dictionary<string, string> variable.

Any suggestion ?
Thanks

dox <(E-Mail Removed)> wrote:
> I'm having trouble using Dictionary classe. I want to use a Dictionary as a
> key for another Dictionary. The following code gives a sample of what I'm
> talking about.
>
> Dictionary myDates = new Dictionary<Dictionary<string, string>, DateTime>();
>
> The 'Add' or 'ContainsKey' methods need a Dictionary<string, string> as a
> (first) parameter, but how to pass this kind of parameter without
> instanciating another Dictionary<string, string> variable.

What would you want to pass in as the parameter? What kind of key are
you wanting to add/test?

To be honest, Dictionary<TKey,TValue> makes a fairly unlikely hash key
- it doesn't override Equals or GetHashCode, so you have no equality
beyond identity.

Could you give more details about what you're trying to actually
achieve? What's the end goal?

--
Jon Skeet - <(E-Mail Removed)>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk

Here is my problem :
I have several server (identified by their names 'Server1', 'Server2'...)
and several message levels ('Information', 'Warning', 'Error'...).
I want for each couple 'server/message level' store the date of the last
message sent. I thougth about a structure like this :

"Server1"/"Information" -> 2008/03/12 14:00:00
"Server1"/"Error" -> 2008/03/11 09:55:00
"Server2"/"Error" -> 2008/02/27 10:11:00
....

In this structure, the key would be a Dictionary<string, string> identifying
the server and the message level. The value would be the DateTime. I know I
could achieve it in an easier way by concatenating the key
("Server1:Information") and using a Dictionary<string, DateTime>. I'm just
wondering if it is possible to use a Dictionary as a key, and how to use it.


"Jon Skeet [C# MVP]" wrote:

> dox <(E-Mail Removed)> wrote:
> > I'm having trouble using Dictionary classe. I want to use a Dictionary as a
> > key for another Dictionary. The following code gives a sample of what I'm
> > talking about.
> >
> > Dictionary myDates = new Dictionary<Dictionary<string, string>, DateTime>();
> >
> > The 'Add' or 'ContainsKey' methods need a Dictionary<string, string> as a
> > (first) parameter, but how to pass this kind of parameter without
> > instanciating another Dictionary<string, string> variable.
>
> What would you want to pass in as the parameter? What kind of key are
> you wanting to add/test?
>
> To be honest, Dictionary<TKey,TValue> makes a fairly unlikely hash key
> - it doesn't override Equals or GetHashCode, so you have no equality
> beyond identity.
>
> Could you give more details about what you're trying to actually
> achieve? What's the end goal?
>
> --
> Jon Skeet - <(E-Mail Removed)>
> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
> World class .NET training in the UK: http://iterativetraining.co.uk
>

dox <(E-Mail Removed)> wrote:
> Here is my problem :
> I have several server (identified by their names 'Server1', 'Server2'...)
> and several message levels ('Information', 'Warning', 'Error'...).
> I want for each couple 'server/message level' store the date of the last
> message sent. I thougth about a structure like this :
>
> "Server1"/"Information" -> 2008/03/12 14:00:00
> "Server1"/"Error" -> 2008/03/11 09:55:00
> "Server2"/"Error" -> 2008/02/27 10:11:00
> ...
>
> In this structure, the key would be a Dictionary<string, string> identifying
> the server and the message level. The value would be the DateTime. I know I
> could achieve it in an easier way by concatenating the key
> ("Server1:Information") and using a Dictionary<string, DateTime>. I'm just
> wondering if it is possible to use a Dictionary as a key, and how to use it.

You still wouldn't use a Dictionary as a key here. You'd use a
dictionary as the *value* of the outermost Dictionary:

Dictionary<string,Dictionary<string,DateTime>> foo;

Then you could do: Console.WriteLine(foo["Server1"]["Information"]).

However, you've already actually given the crux of a much better
solution, without realising it:

"I want for each couple 'server/message level'"

So, you want a type which encapsulates both the server and the message
level, and defines equality and hashcode based on that information
pair.

--
Jon Skeet - <(E-Mail Removed)>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk

You're right. After all, Dictionary as a key is probably not the best solution.
Let's write a custom Type, encapsulating both the server and message level.

Thanks a lot !

"Jon Skeet [C# MVP]" wrote:

> You still wouldn't use a Dictionary as a key here. You'd use a
> dictionary as the *value* of the outermost Dictionary:
>
> Dictionary<string,Dictionary<string,DateTime>> foo;
>
> Then you could do: Console.WriteLine(foo["Server1"]["Information"]).
>
> However, you've already actually given the crux of a much better
> solution, without realising it:
>
> "I want for each couple 'server/message level'"
>
> So, you want a type which encapsulates both the server and the message
> level, and defines equality and hashcode based on that information
> pair.
>
> --
> Jon Skeet - <(E-Mail Removed)>
> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
> World class .NET training in the UK: http://iterativetraining.co.uk
>

dox <(E-Mail Removed)> wrote:
> You're right. After all, Dictionary as a key is probably not the best solution.

Not just that - it's not really a feasible one. Did you see what I
meant about using a dictionary as the first level *value* rather than
key?

> Let's write a custom Type, encapsulating both the server and message level.

That would indeed be the best approach, IMO. Don't forget to override
both Equals and GetHashCode, in a consistent manner.

--
Jon Skeet - <(E-Mail Removed)>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
World class .NET training in the UK: http://iterativetraining.co.uk