[Rd] puzzled by cat() behaviour when argument '...' is a vector (and argument 'sep' contains "\n")

[Duncan Murdoch]

On 05/11/2008 5:47 PM, Peter Ruckdeschel wrote:
> Hi r-devels,
> 
> I am a bit puzzled by the behaviour of  cat() --- any help is appreciated...
> 
> At least AFAICS, cat() for vector-valued '...' argument behaves in
> contradiction to what I understand from the note in the help to cat()
> which reads
> 
> "
> Despite its name and earlier documentation, 'sep' is a vector of
>      terminators rather than separators, being output after every
>      vector element (including the last).  Entries are recycled as
>      needed.
> "

I think you're right that the documentation is incorrect.  I'd prefer a 
patch to the docs, rather than a change to the behaviour:  cat() is so 
fundamental that any changes to it would have wide ranging consequences.

If you want to study the code and draft a documentation patch, I'll 
review it and possibly commit it.

Duncan Murdoch

> ----------------------------------------------------------------------------
> reproducible example code:
> ----------------------------------------------------------------------------
> 
>> cat(rep("x",3), sep = ".")
> x.x.x
> ## no "." appended!
> 
> Things get even worse if "\n" features in the 'sep' vector:
> 
>> cat(rep("x",3),sep = c(".","\n","."))
> x.x
> x
> ## last separator "."  gets swallowed; an non-intended line feed is
> inserted
> 
> ----------------------------------------------------------------------------
> code causing this behaviour
> ----------------------------------------------------------------------------
> ##### "\n"
> 
> I have looked a bit into the source code
>         (lines 468-630 in builtin.c in src/main)
> and found out, as variable pwidth is set to 1 in line 504, i.e.;
> 
>    if (strstr(CHAR(STRING_ELT(sepr, i)), "\n")) nlsep = 1; /* ASCII */
> 
> the code in lines 622-23, i.e.;
>     
>   if ((pwidth != INT_MAX) || nlsep)
>        Rprintf("\n");
> 
> is responsible for the newline. Is this really intended?
> 
> ##### separators, not terminators
> 
> Another look shows that, contrary to what is said in the help file,
> an element of vector 'sep' is /not/ printed out after each element
> of the vector passed as argument '...' to cat(), "including the last"
> --- confer the for-loop over the elements of '...' in lines 596-617
> and the print-out of the separator
> 
>   cat_printsep(sepr, ntot);
> 
> in line 600. Once again: Is this intended?
> 
> A patch fixing my problem would be easy, though might crash
> other much more important code; would you have any
> proposals?
> 
> Best,
> Peter
> 
> -------------------------------------------------------------------
> Version:
>  platform = i386-pc-mingw32
>  arch = i386
>  os = mingw32
>  system = i386, mingw32
>  status = Under development (unstable)
>  major = 2
>  minor = 9.0
>  year = 2008
>  month = 10
>  day = 01
>  svn rev = 46589
>  language = R
>  version.string = R version 2.9.0 Under development (unstable)
> (2008-10-01 r46589)
> 
> Windows XP (build 2600) Service Pack 3
> 
> Locale:
> LC_COLLATE=German_Germany.1252;LC_CTYPE=German_Germany.1252;LC_MONETARY=German_Germany.1252;LC_NUMERIC=C;LC_TIME=German_Germany.1252
> 
> Search Path:
>  .GlobalEnv, package:stats, package:graphics, package:grDevices,
> package:utils, package:datasets, package:methods, Autoloads, package:base
> 
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