On Tue, 20 Jan 2009, Andriy Miranskyy wrote:
Thank you, William! This makes things clearer.
I am trying to create a tiny converter of free text to Tex format. In
order to do that I need to replace all "_" with "\_" and all "&"
with "\&". Could you please tell me, is there a way of doing it using
gsub?
Yes. gsub("([_&])", "\\\\\\1", x) -- but you will also need to escape
$ and %. There are examples in the experimental Rd2tex function in
the development version of R.
Please stop misusing the bug repository to ask questions (and to
report your non-reading of the documentation: this is in ?regex
referenced from ?sub, 'explicitly', pace Bill).
Regards,
Andriy
Monday, January 19, 2009, 6:24:56 PM, you wrote:
-----Original Message-----
From: r-devel-boun...@r-project.org
[mailto:r-devel-boun...@r-project.org] On Behalf Of amira...@uwo.ca
Sent: Monday, January 19, 2009 10:25 AM
To: r-de...@stat.math.ethz.ch
Cc: r-b...@r-project.org
Subject: [Rd] sub and gsub treat \\ incorrectly (PR#13454)
Sub and gsub treat \\ replacement pattern incorrectly
I expect
sub("a","\\", "a", perl=T)
to produce
[1] "\"
instead it generates
[1] ""
On the other hand, if I run
sub("a","\\\\", "a", perl=T)
it correctly outputs
[1] "\\"
The replacement pattern may include \\digit, which means
to put the digit'th parenthesized subexpression into the
replacement. E.g.
> sub("([[:alpha:]]+) +([[:alpha:]]+)", "\\2 \\1", "One two three
four five")
[1] "two One three four five"
> gsub("([[:alpha:]]+) +([[:alpha:]]+)", "\\2 \\1", "One two three
four five")
[1] "two One four three five"
To support this without ambiguity or surprises, \\ is expected
to be followed by a digit (or L or U when perl=TRUE).
When fixed=TRUE then there is no possibility of a parenthesized
subexpression so \\2 is taken literally.
help(gsub) is not explicit about this behavior.
Because I initially made the same mistake, when I wrote the S+
versions of gsub and sub I included a warning when the replacement
included a \\ not followed by a digit:
>> gsub("([[:alpha:]]+) +([[:alpha:]]+)", "\\ \\", "One two three four
five")
[1] " five"
Warning messages:
backslash in replacement argument of substituteString(fixed=F) is
not
followed by backslash or digit, hence backslash is omitted in:
substit\
uteString(pattern = pattern, replacement = replacement, x = x,
extended ....
The same issue applies to gsub.
--please do not edit the information below--
Version:
platform = i386-pc-mingw32
arch = i386
os = mingw32
system = i386, mingw32
status =
major = 2
minor = 8.1
year = 2008
month = 12
day = 22
svn rev = 47281
language = R
version.string = R version 2.8.1 (2008-12-22)
Windows XP (build 2600) Service Pack 2
Locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
Search Path:
.GlobalEnv, package:stats, package:graphics,
package:grDevices, package:utils, package:datasets,
package:methods, Autoloads, package:base
--
Sincerely,
Andriy
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
