Hi,
>From the R user manual, I have a basic understanding of the scope of function
>evaluation but have a harder time understanding how to mess with environments.
My problem can be summarized by the code shown at the bottom:
- the foo function performs some steps including the assignment of default
values to 3 objects: x, y, z
- at some point, I would like to call either the bar1 or bar2 function based
upon the value of the c argument of the foo function. These functions assign
different values to the x, y, z variables.
- then foo should move on and do other cool stuff
Based upon default R scoping, the x, y, and z variables inside the bar1 and
bar2 functions are not in the same environment as the x, y, and z variables
created inside the foo function.
Can I modify the scope of evaluation of bar1 and bar2 so that x, y, and z
created inside the foo function are modified?
PS:
- I know about "<<-" but, in my real code (which I cannot share, sorry), foo is
already called within other functions and x, y, and z variables do not exist in
the top-level environment and are not returned by foo. So "<<-" does not work
(per manual: " Only when <<- has been used in a function that was returned as
the value of another function will the special behavior described here occur. ")
- In my real example, I have a few dozens of variables to transform in bar1 and
bar2 so exporting a list bundling all the transform values then dispatching
them in foo does not seem practical
- currently, my best solution is to save the inner part of bar1 and bar2 in
separate scripts and sourcing them in foo (that does not seem elegant...)
- also, I know that, theoretically, I could put the content of bar1 and bar2
directly in foo, but as the number of cases handled by foo grows, the code will
become way too long and hardly manageable.
Thanks for your help
######################################
bar1 <- function(){
x <- 1
y <- 1
z <- 1
cat(sprintf('bar1: x=%d, y=%d, z=%d\n', x, y, z))
}
bar2 <- function(){
x <- 2
y <- 2
z <- 2
cat(sprintf('bar2: x=%d, y=%d, z=%d\n', x, y, z))
}
foo <- function(a=1, b=2, c=0){
# some setup code
dummy <- a + b
x <- y <- z <- 0
# here is my scope problem
if (c==1) bar1()
if (c==2) bar2()
# some more code
cat(sprintf('foo: x=%d, y=%d, z=%d\n', x, y, z))
}
foo(c=0)
foo(c=1)
foo(c=2)
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