Hi Peng,

If I undertood your point, try this:

x<-runif(10)
y<-runif(10)
z<-runif(10)
w<-runif(10)

myDF<-data.frame(cbind(x,y,z,w))
myDF

myDF[,c("w","z")]


Happy new year

miltinho


On Thu, Dec 31, 2009 at 5:15 PM, Peng Yu <pengyu.ut@gmail.com> wrote:

> I don't see where describes the implementation of '[]'.
>
> For example, if x is a matrix or a data.frame, how the lookup of
> 'colname1' is x[, 'colname1'] executed. Does R perform a lookup in the
> a hash of the colnames? Is the reference O(1) or O(n), where n is the
> second dim of x?
>
> ______________________________________________
> R-help@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<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>

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