On Jun 24, 2013, at 3:27 PM, David Kulp <[email protected]> wrote:
> According to
> http://cran.r-project.org/doc/contrib/Fox-Companion/appendix-scope.pdf and
> other examples online, I am to believe that R resolves variables using
> lexical scoping by following the frames up the call stack. However, that's
> not working for me. For example, the following code, taken from the
> reference above fails instead of returning 7. What am I doing wrong? Thanks!
>
> f <- function(x) { a<-5; g(x) }
> g <- function(y) { y + a }
> f(2)
> Error in g(x) : object 'a' not found
You need to follow the full example code in John's Appendix:
f <- function (x) x + a
# Here 'a' is being defined in the global environment
a <- 10
# As is 'x' here
x <- 5
# Note that 10 + 5 would be 15,
# 12 is returned showing that x = 2 and not x = 5
# is being use within f()
> f(2)
[1] 12
# Here is where your code starts
# missing the preceding code where 'a' was
# defined globally
f <- function(x) { a<-5; g(x) }
g <- function(y) y + a
# Now it works, showing that 'a <- 5' within f() is not part of the
# value returned by g(), which is the goal of John's example code :-)
> f(2)
[1] 12
Regards,
Marc Schwartz
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