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S3 methods for cbind/rbind

4 messages · Gabor Grothendieck, Vincent Goulet

Original
Vincent Goulet
# 
I created a type of object similar to a data frame. In some circumstances, It 
needs special methods for "[" and "[<-" and rbind() (but not cbind()). Then I 
found this in the cbind()/rbind() man page:

     The method dispatching is _not_ done via 'UseMethod()', but by
     C-internal dispatching. Therefore, there is no need for, e.g.,
     'rbind.default'.

This seems to imply I cannot add my own method. Is there 1) a workaround to 
and 2) a rationale for this? (Other than creating a generic Rbind() or 
whatever, that is.)

I'm using S3 methods.

Thanks in advance!
Gabor Grothendieck
# 
Actually you can add your own method.  See

library(zoo)
rbind.zoo

for an example.
On 9/27/06, Vincent Goulet <vincent.goulet at act.ulaval.ca> wrote:
Vincent Goulet
# 
Hum. Then, I need to be more accurate. My object is of class 
c("bar", "data.frame"). So, by virtue of ...

     The dispatch algorithm is described in the source file
     ('.../src/main/bind.c') as

        1.  For each argument we get the list of possible class
           memberships from the class attribute.

        2.  We inspect each class in turn to see if there is an an
           applicable method.

... rbind(foo) is never sent to rbind.bar(). So I guess my questions stand.

Le Mercredi 27 Septembre 2006 16:16, Gabor Grothendieck a ?crit?:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Gabor Grothendieck
    

    

      
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Maybe you could use rbind2, which has an S4 generic in the methods
package, instead?

# BOD is a data frame built into R
foo <- structure(BOD, class = c("bar", "data.frame"))
setOldClass("bar")
setMethod("rbind2", signature(x = "bar", y = "bar"),
	  function(x, y) {
		cat("Hello!\n")
		class(x) <- class(y) <- "data.frame"
		rbind(x, y)
	})

# test
foo <- structure(BOD, class = c("bar", "data.frame"))
rbind2(foo, foo)

        
On 9/27/06, Vincent Goulet <vincent.goulet at act.ulaval.ca> wrote: