[R] About the scope of a variable and the save() method

[Duncan Murdoch]

On 12-09-28 11:51 PM, Qiang Wang wrote:
> In the following test, the variable x is supposed to be modified within the
> function test.save.x. It works as expected util using the save command.
>
> # initialize x.file
> x <- 1
> save(x, file="x.file")
> rm(x) # Remove x from R_GlobalEnv
> exists("x") # FALSE
>
> # define test
> test.save.x <- function(){
> save.x <- function(){
> save(x, file="x.file")
> }
>   change.x <- function(){
> load("x.file", parent.frame(n = 2)) # load x to upper level frame

The upper level frame is globalenv(), so this is the line that creates x.

> x <<- x + 1
> save.x() # If comment this line. x variable will not appear in R_GlobalEnv

This comment is false.  save.x() doesn't create any new variable, it 
just creates a file.


> }
>   change.x()
> }
>
> test.save.x()
> exists("x") # TRUE. Why?

Because you created it by your call to load().

Duncan Murdoch