On 09/17/2009 12:04 PM, Martin Maechler wrote:
"SH" == Schalk Heunis<schalk.heu...@enerweb.co.za>
on Thu, 17 Sep 2009 11:15:16 +0200 writes:
SH> I think this is what you want:
>> df<- data.frame(x1=1:11,x2=2:12,x3=3:13,y=4:14)
>> grep('^x',names(df))
SH> [1] 1 2 3
SH> The returned indexes refer to the column positions, so you could do:
>> names(df)[grep('^x',names(df))]
SH> [1] "x1" "x2" "x3"
yes, or slightly more elegant and efficient
> grep('^x',names(df), value = TRUE)
[1] "x1" "x2" "x3"
or, if you have the operators package:
> require( operators )
> names(df) %~|% "^x"
[1] "x1" "x2" "x3"
... note that is has been declared confusing in this mailing list
previously. http://article.gmane.org/gmane.comp.lang.r.general/154749
SH> or
>> df[,grep('^x',names(df))]
SH> x1 x2 x3
SH> 1 1 2 3
SH> 2 2 3 4
SH> 3 3 4 5
SH> 4 4 5 6
SH> 5 5 6 7
SH> 6 6 7 8
SH> 7 7 8 9
SH> 8 8 9 10
SH> 9 9 10 11
SH> 10 10 11 12
SH> 11 11 12 13
SH> HTH
SH> Schalk Heunis
SH> On Thu, Sep 17, 2009 at 5:03 AM, Peng Yu<pengyu...@gmail.com> wrote:
>> Hi,
>>
>> data.frame(x1=1:11,x2=2:12,x3=3:13,y=4:14)
>>
>> I want to extract all the columns that with the name 'x?'. Is there a
>> general way to do this in R?
>>
>> Regards,
>> Peng
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