R help - Feb 2011 - Getting variable names in function output

Dear R-users,

I would like to have some advises about a problem illustrated by the
following snippet. Within myf, I need to evaluate a piece of R code that is
passed as a character argument and then return the objects that are created
by this code. The difficulty comes from the fact that the content of the
code is variable and unknown to me (obviously not in this illustration!).
With the following script, myf returns the content of the objects created by
the code, but I could not find a way to get the names of the objects in
addition to their contents.

Any suggestion will be welcome

Sebastien

rm(list=ls(all=T))

code1 <- paste('l <- list(a=1,b=2,c=3)',
                       'm <- matrix(1:15,nrow=3)', sep='\n')

code2 <- 'g <- rnorm(100,10,2)'

myf <- function(code=NULL){

  start <- ls(all=T)

  eval(parse(text=code))

  end <- ls(all=T)
  end <- end[-which(end=='start')]

  return(lapply(end[!end%in%
start],function(x) eval(parse(text=x))))
}

myf(code1)
myf(code2)

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I realy think you are on a completely non-R way of implementing 
something that could be done much better. But since I do not know what 
you are going to do, here is the answer for your question:

Just add
   names(end) <- end
one line before your return() statement.

Uwe Ligges




On 03.02.2011 01:55, S?bastien Bihorel wrote:
> Dear R-users,
>
> I would like to have some advises about a problem illustrated by the
> following snippet. Within myf, I need to evaluate a piece of R code that is
> passed as a character argument and then return the objects that are created
> by this code. The difficulty comes from the fact that the content of the
> code is variable and unknown to me (obviously not in this illustration!).
> With the following script, myf returns the content of the objects created
by
> the code, but I could not find a way to get the names of the objects in
> addition to their contents.
>
> Any suggestion will be welcome
>
> Sebastien
>
> rm(list=ls(all=T))
>
> code1<- paste('l<- list(a=1,b=2,c=3)',
>                         'm<- matrix(1:15,nrow=3)',
sep='\n')
>
> code2<- 'g<- rnorm(100,10,2)'
>
> myf<- function(code=NULL){
>
>    start<- ls(all=T)
>
>    eval(parse(text=code))
>
>    end<- ls(all=T)
>    end<- end[-which(end=='start')]
>
>    return(lapply(end[!end%in%
> start],function(x) eval(parse(text=x))))
> }
>
> myf(code1)
> myf(code2)
>
> 	[[alternative HTML version deleted]]
>
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