Gentlemen: I'm sorry, I don't see the problem. R's is Lisp (or Scheme)-inspired, so you need to think in terms of lists, or equivalently, trees. So what you seem to want to do is easily navigate down a tree to modify a node. This is fairly easy to do with list indexing:
## First create a tree with 5 top nodes each of which has 3 child leaf nodes ## each of which is an empty list. fooStack<-lapply(1:5,function(x)lapply(1:3,function(x)list())) ## Now modify the <4,2> leaf list: fooStack[[c(4,2)]]$bar <- "bar" ## Note: This is shorthand for fooStack[[4]][[2]]$bar <- "bar" > fooStack [[1]] [[1]][[1]] list() [[1]][[2]] list() [[1]][[3]] list() [[2]] [[2]][[1]] list() [[2]][[2]] list() [[2]][[3]] list() [[3]] [[3]][[1]] list() [[3]][[2]] list() [[3]][[3]] list() [[4]] [[4]][[1]] list() [[4]][[2]] [[4]][[2]]$bar [1] "bar" [[4]][[3]] list() [[5]] [[5]][[1]] list() [[5]][[2]] list() [[5]][[3]] list() Cheers, Bert Gunter Genentech -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Charilaos Skiadas Sent: Thursday, January 03, 2008 1:46 PM To: Peter Waltman Cc: r-help@r-project.org Subject: Re: [R] Suggestion on how to make permanent changes to a singleobject in a list? You might want to consider using the proto package. Otherwise, functions that end in <- have the ability to alter their arguments. Look at the following (admittedly not very natural) construct: `fooModifier<-` <- function( foo, value ) { foo$bar <- "bar" } fooModifier( fooStack[[ 1 ]] ) <- NULL > fooStack [[1]] [1] "bar" [[2]] list() [[3]] list() [[4]] list() [[5]] list() I agree, that it would be nice to be able to do this more easily. Haris Skiadas Department of Mathematics and Computer Science Hanover College On Jan 3, 2008, at 4:35 PM, Peter Waltman wrote: > > specifically, imagine we have: > > fooStack <- list() > for ( i in 1:5 ) > fooStack[[i]] <- list() > > and we have a function: > > fooModifier <- function( foo ) { > > foo$bar <- "bar" > > } > > then, if we invoke fooModifier, i.e.: > > fooModifier( fooStack[[ 1 ]] ) > > the $bar elt is only set in the scope of the function, and if we > use the > "<<-" modifier in fooModifier, R will throw an error b/c it > can't find the > "foo" object. I have to say that for someone coming from > languages that > have pointers and/or references, it's really frustrating that R > fails to > allow one to have direct access to the objects' memory space. > Onyway, one workaround would be to pass in the whole fooStack > object and the > index of the elt that you want to modify to the fooModifier fn, > but I'd > rather not have to pass the whole thing in. > Any suggestions? > Thanks! > Peter Waltman ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code. ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.
