R help - Nov 2005 - str and structable error

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:
> sss<-structable(Titanic)
> str(sss)
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

Petr Pikal wrote:
> 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:
> 
> 
>>sss<-structable(Titanic)
>>str(sss)
> 
> Error in "[.structable"(x, args[[1]], ) : subscript out of 
> bounds
Looks like package vcd needs a separate structable method for the str() 
generic.

Uwe Ligges


> 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
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

>>>>> "Petr" == Petr Pikal <petr.pikal at
precheza.cz>
>>>>>     on Mon, 28 Nov 2005 08:38:07 +0100 writes:
    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, ...) 
}
> str(structable(Titanic))
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