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

[Juliet Hannah]

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.
>
>