Message-ID: <51117916.5080906@gmail.com>
Date: 2013-02-05T21:26:46Z
From: Duncan Murdoch
Subject: R Regular Expressions - Metacharacters
In-Reply-To: <CAOAmvdxZcuQkAoU91mQGr=Xk9Aam5nKGRMHOY10yF3_8vsj-Mw@mail.gmail.com>
On 05/02/2013 12:49 PM, Seth Dickey wrote:
> I thought that I can use metacharacters such as \w to match word characters
> with one backslash. But for some reason, I need to include two backslashes.
>
> > grepl(pattern='\w', x="what")
> Error: '\w' is an unrecognized escape in character string starting "\w"
>
> > grepl(pattern='\\w', x="what")
> [1] TRUE
>
> I can't find the reason for this on the help pages. Does anyone know why?
grepl wants a string containing a single backslash. R uses the
backslash as an escape character, so you need to double it in your
source, so the string ends up containing just one.
"\w" is interpreted by R as an escaped w, which doesn't make sense.
"\\w" is interpreted by R as a backslash followed by a w, and then the
\w is interpreted by grepl the way you want.
Duncan Murdoch