From ripley at stats.ox.ac.uk  Thu Jan  4 11:42:23 2007
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Thu, 4 Jan 2007 10:42:23 +0000 (GMT)
Subject: [Rd] pb in regular expression with the character "-" (PR#9437)
In-Reply-To: <20070103175522.D1D843F03E@slim.kubism.ku.dk>
References: <20070103175522.D1D843F03E@slim.kubism.ku.dk>
Message-ID: <Pine.LNX.4.64.0701041020150.15115@gannet.stats.ox.ac.uk>

Why do you think this is a bug in R?  You have not told us what you 
expected, but the character range |-| contains only | .  Not agreeing with 
your expectations (unstated or otherwise) is not a bug in R.

\- is the same as -, and - is special in character classes.  (If it is 
first or last it is treated literally.)  And | is not a metacharacter 
inside a character class.  Also,

> grep("[d\\-c]", c("a-a","b"))
[1] 1 2
> grep("[d\\-c]", c("a-a","b"), perl=TRUE)
[1] 1

shows that escaping - works only in perl (which you will find from the 
background references mentioned, e.g.

   The interpretation of an ordinary character preceded by a backslash
   ('\') is undefined.

.)

This is all carefully documented in ?regexp, e.g.

      Patterns are described here as they would be printed by 'cat': do
      remember that backslashes need to be doubled in entering R
      character strings from the keyboard.


This is not the first time you have wasted our resources with false 
bug reports, so please show more respect for the R developers' time.
You were also explicitly asked not to report on obselete versions of R.

On Wed, 3 Jan 2007, xiao.gang.fan1 at libertysurf.fr wrote:

> Full_Name: FAN
> Version: 2.4.0
> OS: Windows
> Submission from: (NULL) (159.50.101.9)
>
>
> These are expected:
>
>> grep("[\-|c]", c("a-a","b"))
> [1] 1
>
>> gsub("[\-|c]", "&", c("a-a","b"))
> [1] "a&a" "b"
>
> but these are strange:
>
>> grep("[d|\-|c]", c("a-a","b"))
> integer(0)
>
>> gsub("[d|\-|c]", "&", c("a-a","b"))
> [1] "a-a" "b"
>
> Thanks
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

-- 
Brian D. Ripley,                  ripley at 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



[Rd] pb in regular expression with the character "-" (PR#9437)
Prof Brian Ripley