Message-ID: <4B015866.10405@stats.uwo.ca>
Date: 2009-11-16T13:49:26Z
From: Duncan Murdoch
Subject: on gsub (simple, but not to me!) sintax
In-Reply-To: <4B0151D2.2070004@unifi.it>
On 11/16/2009 8:21 AM, Ottorino-Luca Pantani wrote:
> Dear R users,
> my problem today deals with my ignorance on regular expressions.
> a matter I recently discovered.
You were close. First, gsub by default doesn't need escapes before the
parens. (There are lots of different conventions for regular
expressions, unfortunately.) So the Emacs regular expression V_\(.\)_
is entered as "V_(.)_" in the default version of gsub(). Second, to
enter a backslash into a string, you need to escape it. So the
replacement pattern V_0\1_ is entered as "V_0\\1_". So
gsub("V_(.)_", "V_0\\1_", foo)
should give you what you want.
Duncan Murdoch
>
> Consider the following
>
> foo <-
> c("V_7_101110_V", "V_7_101110_V", "V_9_101110_V", "V_9_101110_V",
> "V_9_s101110_V", "V_9_101110_V", "V_9_101110_V", "V_11_101110_V",
> "V_11_101110_V", "V_11_101110_V", "V_11_101110_V", "V_11_101110_V",
> "V_17_101110_V", "V_17_101110_V")
>
> what I'm trying to obtain is to add a zero in front of numbers below 10,
> as in
>
> c("V_07_101110_V", "V_07_101110_V", "V_09_101110_V", "V_09_101110_V",
> "V_09_101110_V", "V_09_101110_V", "V_09_101110_V", "V_11_101110_V",
> "V_11_101110_V", "V_11_101110_V", "V_11_101110_V", "V_11_101110_V",
> "V_17_101110_V", "V_17_101110_V")
>
>
> I'm able to do this on the emacs buffer through query-replace-regexp
>
> C-M-%
> search for
> V_\(.\)_
> and substitute with
> V_0\1_
>
> but I completely ignore how to do it with gsub within R
> and the help is quite complicate to understand
> (at least to me, at this moment in time)
>
> I can search the vector through
> grep("V_._", foo)
>
> but I always get errors either on
> gsub('V_\(.\)_', 'V_0\1_', foo)
>
>
> or I get not what I'm looking for on
> gsub('V_._', 'V_0._', foo)
> gsub('V_._', 'V_0\1_', foo)
>
> Thanks in advance