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str and structable error

4 messages · PIKAL Petr, Uwe Ligges, Martin Maechler +1 more

PIKAL Petr
# 
Hallo

I encountered a behaviour which puzzles me (but 
finally I did get what I wanted).

I used structable and strucplot but I wanted to change 
names of variables in structable object. I tried to subset 
it, use names but to no avail. So I tried str and 
expected to get a structure of an object but:
Error in "[.structable"(x, args[[1]], ) : subscript out of 
bounds

Finally I learned, that I need to change attributes of 
structable object.

Is this error message OK and I did not read 
documentation properly? Or is it normal that str gives 
an error on some objects but I just was not so lucky to 
meet one?.

W2000, R2.2.0, vcd package Built: R 2.2.0; ; 2005-11-
22 14:23:44; windows, 

Best regards.

Petr

Petr Pikal
petr.pikal at precheza.cz
Uwe Ligges
#
Petr Pikal wrote:

            

      
      
      
    

        
Looks like package vcd needs a separate structable method for the str() 
generic.

Uwe Ligges

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Martin Maechler
    

    

      
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Petr> Hallo I encountered a behaviour which puzzles me (but
    Petr> finally I did get what I wanted).


    Petr> I used structable and strucplot but I wanted to change
    Petr> names of variables in structable object. 

structable is not "part of R" :
You should tell us that you are using an extra package where
structable is from : namely -- I did your homework -- "vcd"

    Petr> I tried to subset it, use names but to no avail. So I
    Petr> tried str and expected to get a structure of an object
    Petr> but:

    >> sss<-structable(Titanic)
    >> str(sss)
    Petr> Error in "[.structable"(x, args[[1]], ) : subscript
    Petr> out of bounds

yes, and similar problems from

    library(vcd)
    example(structable)
    str(hec)

--> see below

    Petr> Finally I learned, that I need to change attributes of
    Petr> structable object.

    Petr> Is this error message OK and I did not read
    Petr> documentation properly? Or is it normal that str gives
    Petr> an error on some objects but I just was not so lucky
    Petr> to meet one?.

No, it is not normal (and is a bug -- in vcd code IMO):

The reason is that  structable ``objects'' (S3)
do not fulfill a fundamental property that all  S (and hence R)
objects should fulfill IMO  {but read on before protesting}

      >>>>> length() and "[" should be compatible
      >>>>> -------------------------------------

namely, for an object 'x', if
   n <- length(x)
and assume n > 0 for the moment, 
then
   x[j]
should return something reasonable for all numeric vectors 'j'
which have values in {1,2,...,n}  (and  also for {-n,...,-1})

This is unfortunately not at all true for structable objects.
I'd say the authors of "structable" made a bit a peculiar
decision when they designed the "[.structable" method since that
invalidates the above basic principle.
This is particularly unfortunate, since "structable" also
inherits from "ftable" {a ``standard R'' S3 class} which does
not have that bad property

If the current "[" (non-S-like IMO) behavior of structable
objects really will be maintained in the future, 
one solution / workaround would be to define a simple 
str.structable  method -- which would also help you for the
moment :

str.structable <- function(object, ...) { 
   cat("structable ")
   class(object) <- class(object)[-1]
   str(object, ...) 
}

            

      
      
      
    

        
structable  ftable [1:8, 1:4] 0 118 0 154 35 387 0 670 5 57 ...
 - attr(*, "dnames")=List of 4
  ..$ Class   : chr [1:4] "1st" "2nd" "3rd" "Crew"
  ..$ Sex     : chr [1:2] "Male" "Female"
  ..$ Age     : chr [1:2] "Child" "Adult"
  ..$ Survived: chr [1:2] "No" "Yes"
 - attr(*, "split_vertical")= logi [1:4] FALSE  TRUE FALSE  TRUE
 - attr(*, "col.vars")=List of 2
  ..$ Sex     : chr [1:2] "Male" "Female"
  ..$ Survived: chr [1:2] "No" "Yes"
 - attr(*, "row.vars")=List of 2
  ..$ Class: chr [1:4] "1st" "2nd" "3rd" "Crew"
  ..$ Age  : chr [1:2] "Child" "Adult"
 - attr(*, "class")= chr "ftable"

            

      
      
      
    

        
Regards,
Martin Maechler, ETH Zurich


    Petr> W2000, R2.2.0, vcd package Built: R 2.2.0; ; 2005-11-
    Petr> 22 14:23:44; windows,

    Petr> Best regards.

    Petr> Petr

    Petr> Petr Pikal petr.pikal at precheza.cz

  
  


  


      

    

    

      
      

        


  

        

      David Meyer
    

    

      
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I tried to subset

            

      
      
      
    

        
yes! Thanks for pointing this out. It's because "[.structable" has a
non-standard behavior. Using:

"[.structable" = function(object, ...) NextMethod()

at the command line, str() would work as expected.

David