R help - Aug 2010 - how to implement string pattern extraction in R

Hi,

In perl, to get a substring matching a particular  pattern can be
implemented like the following example:

$x = "AAAA.txt";
if ($x=~ /(.*?)\.txt/){
  $prefix = $1;
}

So how to do the same thing in R?

Can someone provide me the code sample?

Thanks much in advance.

-- 
Waverley @ Palo Alto

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org]
> On Behalf Of Waverley @ Palo Alto
> Sent: Sunday, August 22, 2010 3:05 PM
> To: r-help
> Subject: [R] how to implement string pattern extraction in R
> 
> Hi,
> 
> In perl, to get a substring matching a particular  pattern can be
> implemented like the following example:
> 
> $x = "AAAA.txt";
> if ($x=~ /(.*?)\.txt/){
>   $prefix = $1;
> }
> 
> So how to do the same thing in R?
> 
> Can someone provide me the code sample?
> 
> Thanks much in advance.
> 
> --
> Waverley @ Palo Alto
> 
Check out the documentation for regexp

?regexp

Hope this is helpful,

Dan

Daniel Nordlund
Bothell, WA USA

Hi Waverley,

I am not familiar at all with perl, but this should get you headed in
the right direction:

#Some documentation that might help
?regexpr
?grep
?regexp


#I imagine you sould do something like

x <- "AAAA.txt"
regexpr(pattern = "yourpattern", text = x)
grep(pattern = "yourpattern", x = x)

#also note the "perl =" argument you can set in regexpr()

Cheers,

Josh

On Sun, Aug 22, 2010 at 3:05 PM, Waverley @ Palo Alto
<waverley.paloalto at gmail.com> wrote:
> Hi,
>
> In perl, to get a substring matching a particular ?pattern can be
> implemented like the following example:
>
> $x = "AAAA.txt";
> if ($x=~ /(.*?)\.txt/){
> ?$prefix = $1;
> }
>
> So how to do the same thing in R?
>
> Can someone provide me the code sample?
>
> Thanks much in advance.
>
> --
> Waverley @ Palo Alto
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

On Sun, Aug 22, 2010 at 6:05 PM, Waverley @ Palo Alto
<waverley.paloalto at gmail.com> wrote:
> Hi,
>
> In perl, to get a substring matching a particular ?pattern can be
> implemented like the following example:
>
> $x = "AAAA.txt";
> if ($x=~ /(.*?)\.txt/){
> ?$prefix = $1;
> }
>
> So how to do the same thing in R?
>
> Can someone provide me the code sample?
>
Try any of these:

x <- "AAAA.txt"

# 1
sub("(.*)\\.txt", "\\1", x)

# 2
sub(".txt$", "", x)

# 3
strsplit(x, "\\.")[[1]][1]

#4
library(gsubfn)
strapply(x, "(.*)\\.txt", simplify = c)

Thanks for the reply to pointing me to the grep functions.

I have checked the readme page
http://pbil.univ-lyon1.fr/library/base/html/grep.html before I sent
the help request.

Just don't know how to extract a substring matching a pattern out of a
string.  Can someone give me the example code similar to that in perl
to extract the prefix out of the string.

Thanks much.

On Sun, Aug 22, 2010 at 3:05 PM, Waverley @ Palo Alto
<waverley.paloalto at gmail.com> wrote:
> Hi,
>
> In perl, to get a substring matching a particular ?pattern can be
> implemented like the following example:
>
> $x = "AAAA.txt";
> if ($x=~ /(.*?)\.txt/){
> ?$prefix = $1;
> }
>
> So how to do the same thing in R?
>
> Can someone provide me the code sample?
>
> Thanks much in advance.
>
> --
> Waverley @ Palo Alto
>


-- 
Waverley @ Palo Alto