R help - Jun 2010 - Identify and extract a whole word of variable length using regular expressions

Hi everybody,

I'm quite weak with regular expression, and I need some help...
I have strings of the type
>a
[1,] "ppe46 Rv3018c MT3098/MT3101 MTV012.32c"
[2,] "ppe16 Rv1135c MT1168"                  
[3,] "ppe21 Rv1548c MT1599 MTCY48.17"        
[4,] "ppe12 Rv0755c MT0779"                  
[5,] "PE_PGRS51 Rv3367"                      
[etc..for several hundreds]

I want have instead only:

[1,] "Rv3018c"

[2,] "Rv1135c"                  

[3,] "Rv1548c"        

[4,] "Rv0755c"                  

[5,] "Rv3367"                      


Besides these examples, the only thing I know for sure is that the
"magic" substrings I want to extract are entire word all starting by
"Rv". So "Rvxxxxx", preceded and followed by a space, and of
a variable length. I don't have any other infos.

Do you know how to pick them? I checked for their presence using grep, and
"\\<Rv*\\>" expression, I tried with some string functions from
Hmisc, or in the other way, by substituting with empty strings everything except
the Rv word, but I didn't achieve that much...
Could you please give me some suggestions?

Thanks a lot,


Giulio
 		 	   		  
_________________________________________________________________


	[[alternative HTML version deleted]]

Giulio -
    This
> sub('^.* ?(Rv[^ ]*) ?.*$','\\1',a)
[1] "Rv3018c" "Rv1135c" "Rv1548c"
"Rv0755c" "Rv3367"

seems to do what you want.
 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu


On Mon, 28 Jun 2010, Giulio Di Giovanni wrote:
>
>
> Hi everybody,
>
> I'm quite weak with regular expression, and I need some help...
> I have strings of the type
>
>> a
>
> [1,] "ppe46 Rv3018c MT3098/MT3101 MTV012.32c"
> [2,] "ppe16 Rv1135c MT1168"
> [3,] "ppe21 Rv1548c MT1599 MTCY48.17"
> [4,] "ppe12 Rv0755c MT0779"
> [5,] "PE_PGRS51 Rv3367"
> [etc..for several hundreds]
>
> I want have instead only:
>
> [1,] "Rv3018c"
>
> [2,] "Rv1135c"
>
> [3,] "Rv1548c"
>
> [4,] "Rv0755c"
>
> [5,] "Rv3367"
>
>
> Besides these examples, the only thing I know for sure is that the
"magic" substrings I want to extract are entire word all starting by
"Rv". So "Rvxxxxx", preceded and followed by a space, and of
a variable length. I don't have any other infos.
>
> Do you know how to pick them? I checked for their presence using grep, and
"\\<Rv*\\>" expression, I tried with some string functions from
Hmisc, or in the other way, by substituting with empty strings everything except
the Rv word, but I didn't achieve that much...
> Could you please give me some suggestions?
>
> Thanks a lot,
>
>
> Giulio
>
> _________________________________________________________________
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>

On Mon, Jun 28, 2010 at 7:17 PM, Giulio Di Giovanni
<perimessaggini at hotmail.com> wrote:
>
>
> Hi everybody,
>
> I'm quite weak with regular expression, and I need some help...
> I have strings of the type
>
>>a
>
> [1,] "ppe46 Rv3018c MT3098/MT3101 MTV012.32c"
> [2,] "ppe16 Rv1135c MT1168"
> [3,] "ppe21 Rv1548c MT1599 MTCY48.17"
> [4,] "ppe12 Rv0755c MT0779"
> [5,] "PE_PGRS51 Rv3367"
> [etc..for several hundreds]
>
> I want have instead only:
>
> [1,] "Rv3018c"
>
> [2,] "Rv1135c"
>
> [3,] "Rv1548c"
>
> [4,] "Rv0755c"
>
> [5,] "Rv3367"
>
>
> Besides these examples, the only thing I know for sure is that the
"magic" substrings I want to extract are entire word all starting by
"Rv". So "Rvxxxxx", preceded and followed by a space, and of
a variable length. I don't have any other infos.
>
> Do you know how to pick them? I checked for their presence using grep, and
"\\<Rv*\\>" expression, I tried with some string functions from
Hmisc, or in the other way, by substituting with empty strings everything except
the Rv word, but I didn't achieve that much...
> Could you please give me some suggestions?
>
You can use strapply in gsubfn to pick out strings by content.  The
regular expression says match a word bound followed by R followed by v
followed by 0 or more non-spaces:

library(gsubfn)
strapply(a, "\\bRv\\S*", c, perl = TRUE, simplify = TRUE)