[R] gsub warning message

Talbot Katz topkatz at msn.com
Fri Aug 31 20:30:24 CEST 2007

Thank you for the swift response.  It looks like the code works the same way 
with or without the "\\" in either the search string: { "\\_+" or "_+" }  or 
the replacement string: { "\\." or "." }.  I tested this in Windows and 
Linux (although we're still on R 2.4.1 in Linux).  It's not clear to me why 
I can use either two slashes or no slash safely, but not one slash, and it 
makes me vaguely uneasy.  Obviously, I need to review regular expressions, 
but my usual sources, such as http://perldoc.perl.org/perlre.html, don't 
seem to address this issue.  I wonder whether there's a good document 
explaining this.

--  TMK  --
212-460-5430	home
917-656-5351	cell

>From: Uwe Ligges <ligges at statistik.uni-dortmund.de>
>To: Talbot Katz <topkatz at msn.com>
>CC: r-help at stat.math.ethz.ch
>Subject: Re: [R] gsub warning message
>Date: Fri, 31 Aug 2007 18:04:39 +0200
>Talbot Katz wrote:
>>I am using R 2.5.1 on a Windows XP machine.  Here is an example of a piece 
>>of code I was running in older versions of R on the same machine.  I am 
>>looking for underscores and replacing them with periods.  This result is 
>>from R 2.4.1:
>>>gsub ( "\\_+","\.","AAA_I")
>>[1] "AAA.I"
>>Here is what I get in R 2.5.1:
>>>gsub ( "\\_+","\.","AAA_I")
>>[1] "AAA.I"
>>Warning messages:
>>1: '\.' is an unrecognized escape in a character string
>>2: unrecognized escape removed from "\."
>>I still get the same result, which is what I want, but now I get a warning 
>>message.  Am I actually doing something wrong that the previous versions 
>>of R didn't warn me about?  Or is this warning message unwarranted?  Is 
>>there a fully approved method for getting the same functionality?  Thanks!
>Yes, correct usage is either
>   gsub ( "\\_+", ".", "AAA_I")
>   gsub ( "\\_+", "\\.", "AAA_I")
>Uwe Ligges
>>--  TMK  --
>>212-460-5430	home
>>917-656-5351	cell
>>R-help at stat.math.ethz.ch mailing list
>>PLEASE do read the posting guide 
>>and provide commented, minimal, self-contained, reproducible code.

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