On Thu, Aug 26, 2010 at 12:04 AM, Stephen T. <obsessiv...@hotmail.com> wrote:
>
> Hi, I wanted to create a list of closures. When I use Map(), mapply(),
> lapply(), etc., to create this list, it appears that the wrong arguments are
> being passed to the main function. For example:
> Main function:
>> adder <- function(x) function(y) x + y
> Creating list of closures with Map():
>> plus <- Map(adder,c(one=1,two=2))> plus$one(1)[1] 3> plus$two(1)[1] 3
> Examining what value was bound to "x":
>> Map(function(fn) get("x",environment(fn)),plus)$one[1] 2$two[1] 2
>
> This is what I had expected:
>> plus <- list(one=adder(1),two=adder(2))> plus$one(1)[1] 2> plus$two(1)[1] 3
>> Map(function(fn) get("x",environment(fn)),plus)$one[1] 1$two[1] 2
>
> Anyone know what's going on? Thanks much!
R uses lazy evaluation of function arguments. Try forcing x:
> adder <- function(x) { force(x); function(y) x + y }
> plus <- Map(adder,c(one=1,two=2))
> plus$one(1)
[1] 2
> plus$two(1)
[1] 3
______________________________________________
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.
