[R] renaming objects

[Nordlund, Dan (DSHS/RDA)]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Rolf Turner
> Sent: Monday, March 03, 2008 4:37 PM
> To: hadley wickham
> Cc: r-help; Giles.Crane at doh.state.nj.us
> Subject: Re: [R] renaming objects
> 
> 
> On 4/03/2008, at 11:48 AM, hadley wickham wrote:
> 
> > On Mon, Mar 3, 2008 at 4:37 PM, Rolf Turner  
> > <r.turner at auckland.ac.nz> wrote:
> >>
> >>  On 4/03/2008, at 10:38 AM, Ericka Lundström wrote:
> >>
> >>> On 03/03/2008, at 22.20, Giles.Crane at doh.state.nj.us wrote:
> >>>> Is there a way to rename R objects?
> >>>> I am looking for a way to rename objects
> >>>> without making new objects.
> >>>>
> >>>> #For example:
> >>>> x = c(1:40)
> >>>> # I wish to use a function to rename x, already created, to y,
> >>>> perhaps by
> >>>> obj.rename(x,y)
> >>>> # or
> >>>> obj.rename("x","y")
> >>> y <- x # changes x to y with same values.
> >>
> >>         That makes a new object --- which is precisely what the  
> >> enquirer
> >>         wanted ***NOT*** to do.
> >
> > It doesn't though!
> >
> >> gc()
> >          used (Mb) gc trigger (Mb) max used (Mb)
> > Ncells 133095  3.6     350000  9.4   350000  9.4
> > Vcells  87049  0.7     786432  6.0   478831  3.7
> >> a <- runif(1e7)
> >> gc()
> >            used (Mb) gc trigger (Mb) max used (Mb)
> > Ncells   133112  3.6     350000  9.4   350000  9.4
> > Vcells 10087364 77.0   11458389 87.5 10087374 77.0
> >> b <- a
> >> gc()
> >            used (Mb) gc trigger (Mb) max used (Mb)
> > Ncells   133117  3.6     350000  9.4   350000  9.4
> > Vcells 10087365 77.0   12111308 92.5 10087476 77.0
> >
> > R will only create a copy if either of a or b is modified.
> 
> Well RMIHATMTTL!!!  R is even cleverer than I thought!!!
> 
> 		cheers,
> 
> 			Rolf

But, the OP should know that in the above scenario, if a or b is changed the copy will be created, doubling the storage requirements.  Of course, this can be prevented by removing vector a after the assignment.

Hope this is helpful,

Dan  


Daniel J. Nordlund
Research and Data Analysis
Washington State Department of Social and Health Services
Olympia, WA  98504-5204