On Jul 27, 2012, at 11:23 , Stéphane Dray wrote:
> Dear list,
>
> I try to use the eval function and to understand its functionning. I tried:
>
> xy <- "global"
>
> f1 <- function(){
> xy <- "f1"
> a1 <- eval.parent(xy)
> b1 <- eval(xy, sys.frame(0))
> print(paste("a1 =",a1))
> print(paste("b2 =",b1))
>
> f3 <- function(){
> print("----F3----")
> a3 <- eval.parent(xy)
> b3 <- eval(xy, sys.frame(0))
> print(paste("a3 =",a3))
> print(paste("b3 =",b3))
> }
>
> f2()
> f3()
> }
>
>
> f2 <- function(){
> print("----F2----")
> a2 <- eval.parent(xy)
> b2 <- eval(xy, sys.frame(0))
> print(paste("a2 =",a2))
> print(paste("b2 =",b2))
> }
>
> f1()
> f2()
>
>
> I obtain the following results (and add as comments what I would expect after
> reading the doc). I really do not understand why the evaluation in
> sys.frame(0) (i.e. global environment) did not work. Moreover, the evaluation
> through eval.parent should be linked to the environment of the caller and not
> the definition (so I do not understand why f2 and f3 produces different
> results).
>
> > f1()
> [1] "a1 = f1" ## global ?
> [1] "b2 = f1" ## global
> [1] "----F2----"
> [1] "a2 = global" ## f1
> [1] "b2 = global" ## global
> [1] "----F3----"
> [1] "a3 = f1" ## f1
> [1] "b3 = f1" ## global
> > f2()
> [1] "----F2----"
> [1] "a2 = global"
> [1] "b2 = global"
>
>
>
> Any help would be appreciated, Thanks.
Try quote(xy) in a number of places....
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
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