Re: [R] how to extract the 1st field from a vector of strings

From: Henrique Dallazuanna <wwwhsd_at_gmail.com>
Date: Mon, 31 May 2010 14:07:06 -0300

My mistake:

"\\1" is a backreference - see replacement argument in ?gsub.

This work:
gsub("(.*) MIMA.*", "\\1", desc)

On Mon, May 31, 2010 at 2:00 PM, Juliet Hannah <juliet.hannah_at_gmail.com>wrote:

> What is the meaning of "\\1" here? Thanks.
>
> desc <- c("hsa-let-7a MIMAT0000062 Homo sapiens let-7a","hsa-let-7a*
> MIMAT0004481 Homo sapiens let-7a*","hsa-let-7a-2* MIMAT0010195 Homo
> sapiens let-7a-2*")
>
> I'm missing something:
>
> > gsub(" MIMA.*", "\\1", desc)
> [1] "hsa-let-7a" "hsa-let-7a*" "hsa-let-7a-2*"
> > gsub(" MIMA.*", "\\2", desc)
> [1] "hsa-let-7a" "hsa-let-7a*" "hsa-let-7a-2*"
> > gsub(" MIMA.*", "\\3", desc)
> [1] "hsa-let-7a" "hsa-let-7a*" "hsa-let-7a-2*"
>
> On Thu, May 27, 2010 at 10:58 AM, Henrique Dallazuanna <wwwhsd_at_gmail.com>
> wrote:
> > Try this:
> >
> > gsub(" MIMA.*", "\\1", desc)
> >
> > On Thu, May 27, 2010 at 11:37 AM, <mauede_at_alice.it> wrote:
> >
> >> I have the following vector of strings (shown only the first 3 elements)
> >>
> >> > desc[1:3]
> >> [1] "hsa-let-7a MIMAT0000062 Homo sapiens let-7a"
> >> [2] "hsa-let-7a* MIMAT0004481 Homo sapiens let-7a*"
> >> [3] "hsa-let-7a-2* MIMAT0010195 Homo sapiens let-7a-2*"
> >> > is.vector(desc)
> >> [1] TRUE
> >> > A <- unlist(strsplit(desc[1:3], " "))
> >> > A
> >> [1] "hsa-let-7a MIMAT0000062 Homo sapiens let-7a"
> >> [2] "hsa-let-7a* MIMAT0004481 Homo sapiens let-7a*"
> >> [3] "hsa-let-7a-2* MIMAT0010195 Homo sapiens let-7a-2*"
> >> > as.vector(A)
> >> [1] "hsa-let-7a MIMAT0000062 Homo sapiens let-7a"
> >> [2] "hsa-let-7a* MIMAT0004481 Homo sapiens let-7a*"
> >> [3] "hsa-let-7a-2* MIMAT0010195 Homo sapiens let-7a-2*"
> >> >
> >> I would like to extract only the first field (of variable length). That
> is
> >> I need a vector containing
> >> "hsa-let-7a "
> >> "hsa-let-7a*"
> >> "hsa-let-7a-2*"
> >>
> >> The operator [[]][] works only on the single vector element. I would
> like
> >> to extract the 1st field
> >> with one single instruction rather than a loop as traditional
> programming
> >> languages request.
> >>
> >> Thank you in advance for you help.
> >> Maura
> >>
> >>
> >>
> >> tutti i telefonini TIM!
> >>
> >>
> >> [[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.
> >>
> >
> >
> >
> > --
> > Henrique Dallazuanna
> > Curitiba-Paraná-Brasil
> > 25° 25' 40" S 49° 16' 22" O
> >
> > [[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.
> >
> >
>

-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]


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Received on Mon 31 May 2010 - 17:09:38 GMT

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