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?
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
