[R] Extract Element of String with R's Regex

[Stephen Tucker]

In the example below, a straight application of strsplit() is probably the simplest solution. In a more general case where it may be desirable to match patterns, a combination of sub() or gsub() with strsplit() might do the trick:

> x <- "Best-K Gene 11340 211952_at RANBP5 Noc= 3 - 2 LL= -963.669 -965.35"
> patt <- "Best-K Gene \\d+ (\\w+) (\\w+) Noc= \\d - (\\d) LL= (.*)"

> unlist(strsplit(gsub(patt,"\\1,\\2,\\3",x,perl=TRUE),","))
[1] "211952_at" "RANBP5"    "2"  

Alternatively, you may want to take a look at the gsubfn package - it is quite useful. Still learning to use it myself...

> library(gsubfn)
> unlist(strapply(x,patt,function(x1,x2,x3) c(x1,x2,x3),backref=-3,perl=TRUE))
[1] "211952_at" "RANBP5"    "2"  





----- Original Message ----
From: Simon Blomberg <s.blomberg1 at uq.edu.au>
To: Edward Wijaya <ewijaya at gmail.com>
Cc: r-help at r-project.org
Sent: Thursday, July 31, 2008 11:48:23 PM
Subject: Re: [R] Extract Element of String with R's Regex

How about:

unlist(strsplit(x, split=" "))[c(4:5,10)]

That perl script looks like a good reason to avoid perl.

Simon.

On Fri, 2008-08-01 at 15:13 +0900, Edward Wijaya wrote:
> Hi,
> 
> I have this string, in which I want to extract some of it's element:
> 
> > x <- "Best-K Gene 11340 211952_at RANBP5  Noc= 3 - 2  LL= -963.669 -965.35"
> 
> yielding this array
> 
> [1] "211952_at"  "RANBP5" "2"
> 
> 
> 
> In Perl we would do it this way:
> 
> __BEGIN__
> my @needed =();
> my $str = "Best-K Gene 11340 211952_at RANBP5  Noc= 3 - 2  LL=
> -963.669 -965.35";
> $str =~ /Best-K Gene \d+ (\w+) (\w+) Noc= \d - (\d) LL= (.*)/;
> push @needed, ($1,$2,$3);
> __END___
> 
> How can we achieve this with R?
> 
>  - E.W.
> 
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-- 
Simon Blomberg, BSc (Hons), PhD, MAppStat. 
Lecturer and Consultant Statistician 
Faculty of Biological and Chemical Sciences 
The University of Queensland 
St. Lucia Queensland 4072 
Australia
Room 320 Goddard Building (8)
T: +61 7 3365 2506
http://www.uq.edu.au/~uqsblomb
email: S.Blomberg1_at_uq.edu.au

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