R help - Feb 2010 - S4 programming

Dear all,

I'm new to S4 classes and have a question on this. I want to use S4 because
I want to define explicitly the slots that the new class can have. But other
than that, the new class behaves exactly like a list. But this will not allow me
to use the generic functions that are already defined for class
"list", such as "$", "c", "[[", 
"names" or "length".

For example, I defined a new class "abc", and tried to use
"$", "length", and "[[", but they do not work
(which is shown below). I know I could define these methods for the new class,
but is there an easy way to allow this new class to inherit  all the functions
that work for class "list"? I tried to use contains="list",
but this does not work either. Thanks for any help.
> setClass("abc",
representation(x="numeric",y="character",z="numeric"))
[1] "abc"
> xxx=new("abc",x=1,y="a",z=2)
> xxx$a
Error in xxx$a : $ operator not defined for this S4
class
> length(xxx)
[1] 1
> xxx[[1]]
Error in xxx[[1]] : this S4 class is not subsettable



Wayne (Yanwei) Zhang
Statistical Research
CNA





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On Thu, Feb 25, 2010 at 11:12 PM, Zhang,Yanwei <Yanwei.Zhang at cna.com>
wrote:
>
> Dear all,
>
> I'm new to S4 classes and have a question on this. I want to use S4
because I want to define explicitly the slots that the new class can have. But
other than that, the new class behaves exactly like a list. But this will not
allow me to use the generic functions that are already defined for class
"list", such as "$", "c", "[[",
?"names" or "length".
>
> For example, I defined a new class "abc", and tried to use
"$", "length", and "[[", but they do not work
(which is shown below). I know I could define these methods for the new class,
but is there an easy way to allow this new class to inherit ?all the functions
that work for class "list"? I tried to use contains="list",
but this does not work either. Thanks for any help.
>
>> setClass("abc",
representation(x="numeric",y="character",z="numeric"))
> [1] "abc"
>> xxx=new("abc",x=1,y="a",z=2)
>> xxx$a
> Error in xxx$a : $ operator not defined for this S4 class
>> length(xxx)
> [1] 1
>> xxx[[1]]
> Error in xxx[[1]] : this S4 class is not subsettable
>
>
>
> Wayne (Yanwei) Zhang
> Statistical Research
> CNA
>
>
>
>
>
> NOTICE: ?This e-mail message, including any attachments and appended
messages, is for the sole use of the intended recipients and may contain
confidential and legally privileged information.
> If you are not the intended recipient, any review, dissemination,
distribution, copying, storage or other use of all or any portion of this
message is strictly prohibited.
> If you received this message in error, please immediately notify the sender
by reply e-mail and delete this message in its entirety.
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
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-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O