R help - Feb 2010 - New methods for generic functions show and print : some visible with ls(), some not

Dear all,

I'm trying to understand the S4 way of object-oriented programming, but I
still can't grasp completely what R is doing. I have a class definition for
a class called PM10Meteo, and I set a initializer function. next, I include
a show method and a print method as shown below.

setClass( Class="PM10Meteo",...) # end setClass

setMethod ("initialize",signature="PM10Meteo",...) # end
setMethod

########
# Show Method
#
setMethod("show","PM10Meteo",
  function(object){
...
  } # end function
) # end show method

#######
# Print Method
#

setMethod("print","PM10Meteo",
  function(x,n=400,station=F,values=T,meteo=T,...){
...
  }
) # end print method

Now when I run the complete class definition file, neither the method
"initialize" nor the method "show" occur in the list given
by ls(). On the
other hand, the method "print" does! So when I use rm(list=ls()) I
still
have the "initialize" and "show" method, but the
"print" method is gone. Am
I forgetting something somewhere? It's rather inconvenient to have to run
the definition files every time I want to clear the memory.

Cheers
Joris
-- 
Joris Meys
Statistical Consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

Coupure Links 653
B-9000 Gent

tel : +32 9 264 59 87
Joris.Meys@Ugent.be
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On 26.02.2010 19:04, Joris Meys wrote:
> Dear all,
>
> I'm trying to understand the S4 way of object-oriented programming, but
I
> still can't grasp completely what R is doing. I have a class definition
for
> a class called PM10Meteo, and I set a initializer function. next, I include
> a show method and a print method as shown below.
>
> setClass( Class="PM10Meteo",...) # end setClass
>
> setMethod ("initialize",signature="PM10Meteo",...) #
end setMethod
>
> ########
> # Show Method
> #
> setMethod("show","PM10Meteo",
>    function(object){
> ...
>    } # end function
> ) # end show method
>
> #######
> # Print Method
> #
>
> setMethod("print","PM10Meteo",
>    function(x,n=400,station=F,values=T,meteo=T,...){
> ...
>    }
> ) # end print method

print is not a S4 generic. show methods are mapped to print for 
convenience, though.

Uwe Ligges


> Now when I run the complete class definition file, neither the method
> "initialize" nor the method "show" occur in the list
given by ls(). On the
> other hand, the method "print" does! So when I use rm(list=ls())
I still
> have the "initialize" and "show" method, but the
"print" method is gone. Am
> I forgetting something somewhere? It's rather inconvenient to have to
run
> the definition files every time I want to clear the memory.
>
> Cheers
> Joris

On 26/02/2010 1:04 PM, Joris Meys wrote:
> Dear all,
>
> I'm trying to understand the S4 way of object-oriented programming, but
I
> still can't grasp completely what R is doing. I have a class definition
for
> a class called PM10Meteo, and I set a initializer function. next, I include
> a show method and a print method as shown below.
>
> setClass( Class="PM10Meteo",...) # end setClass
>
> setMethod ("initialize",signature="PM10Meteo",...) #
end setMethod
>
> ########
> # Show Method
> #
> setMethod("show","PM10Meteo",
>   function(object){
> ...
>   } # end function
> ) # end show method
>
> #######
> # Print Method
> #
>
> setMethod("print","PM10Meteo",
>   function(x,n=400,station=F,values=T,meteo=T,...){
> ...
>   }
> ) # end print method
>
> Now when I run the complete class definition file, neither the method
> "initialize" nor the method "show" occur in the list
given by ls(). On the
> other hand, the method "print" does! So when I use rm(list=ls())
I still
> have the "initialize" and "show" method, but the
"print" method is gone. Am
> I forgetting something somewhere? It's rather inconvenient to have to
run
> the definition files every time I want to clear the memory.
You aren't seeing the print method, you are seeing a newly created print 
generic function.  As Uwe mentioned, print() is not an S4 generic, so 
when you create your print method, a new S4 generic also gets created.  
You should be using show(), which will be called by print() when necessary.

When you say "clear the memory", I'm not sure what you have in
mind, but
S4 methods are not stored in your workspace, so rm(list=ls()) won't 
delete them.  You need removeMethod() to get rid of a method.

Duncan Murdoch