R help - May 2011 - Using GSUB to obtain a printing "\"

Hello. I'd like to be able to print variable strings which contain
"\" as-is, without interpreting (for example) "abcde\nuvxyz"
as having an embedded newline (or whatever other escaped instruction).

To do this, I've tried gsub, and here's some of my output (I've
tried all kinds of variations to the arguments):
> message(gsub("[\\]","\\\\","dsff\nfsd"))
dsff
fsd

but I would like to see:
dsff\nfsd? 
(which is the output of message("dsff\\nfsd") )

I don't know why gsub doesn't accomplish this substitution. How can I
replace (for example), a "\" with "\\"? Any suggestions
would be greatly appreciated. (I know I can use another language, or use
inelegant brute force by writing a new routine which cycles through each
possible character that could follow the single "\".) Watching the
gsub echo at the R prompt shows that it is gsub (and not message) not behaving
as I expected.


Other information which the posting guidelines say might
help:
> sessionInfo()
R version 2.13.0 (2011-04-13)
Platform: x86_64-apple-darwin10.7.0/x86_64 (64-bit)

locale:
[1] C

attached base packages:
[1] stats???? graphics? grDevices utils???? datasets? methods? ?base???? 

other attached packages:
[1] Rd2roxygen_0.1-8 roxygen_0.1-2??? digest_0.4.2??? 

loaded via a namespace (and not attached):
[1] tools_2.13.0
> Sys.getlocale()
[1] "C"

Thanks very much!

gsub does this because the string "dsff\nfsd"
does not contain a backslash - the 5th character
is a newline.  The deparsed representation (used
for printing the string) of a newline is "\n" but
the string itself has not backslash.

You can feed the output of deparse into message (or
cat) so they show the backslash-n characters, but
you then have to remove the enclosing quotes that
deparse adds.

  > x<-"dsff\nfs\rd\1"
  > x
  [1] "dsff\nfs\rd\001"
  > message("x is ", deparse(x))
  x is "dsff\nfs\rd\001"
  > message("x is ", gsub("^\"|\"$",
"", deparse(x)))
  x is dsff\nfs\rd\001
  > cat("x is", gsub("^\"|\"$", "",
deparse(x)), "\n")
  x is dsff\nfs\rd\001 
  > cat(x) # this is with Windows Rgui.exe
  dsff
  fs
  d> 

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Bhushan, Vipul
> Sent: Thursday, May 05, 2011 2:48 PM
> To: r-help at r-project.org
> Subject: [R] Using GSUB to obtain a printing "\"
> 
> Hello. I'd like to be able to print variable strings which 
> contain "\" as-is, without interpreting (for example) 
> "abcde\nuvxyz" as having an embedded newline (or whatever 
> other escaped instruction). 
> 
> To do this, I've tried gsub, and here's some of my output 
> (I've tried all kinds of variations to the arguments): 
> 
> > message(gsub("[\\]","\\\\","dsff\nfsd"))
> dsff
> fsd
> 
> but I would like to see:
> dsff\nfsd? 
> (which is the output of message("dsff\\nfsd") )
> 
> I don't know why gsub doesn't accomplish this substitution. 
> How can I replace (for example), a "\" with "\\"? Any 
> suggestions would be greatly appreciated. (I know I can use 
> another language, or use inelegant brute force by writing a 
> new routine which cycles through each possible character that 
> could follow the single "\".) Watching the gsub echo at the R 
> prompt shows that it is gsub (and not message) not behaving 
> as I expected. 
> 
> 
> Other information which the posting guidelines say might help:
> > sessionInfo()
> R version 2.13.0 (2011-04-13)
> Platform: x86_64-apple-darwin10.7.0/x86_64 (64-bit)
> 
> locale:
> [1] C
> 
> attached base packages:
> [1] stats???? graphics? grDevices utils???? datasets? methods?
>  ?base???? 
> 
> other attached packages:
> [1] Rd2roxygen_0.1-8 roxygen_0.1-2??? digest_0.4.2??? 
> 
> loaded via a namespace (and not attached):
> [1] tools_2.13.0
> > Sys.getlocale()
> [1] "C"
> 
> Thanks very much!
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>