Dear all,
I quickly checked on the internet and nothing relevant came up, so, I
hope to find the answer to a question here. I'd pleased to be
redirected towards relevant pieces of information on the internet, if I
merely missed something obvious.
Actually, I've got two somewhat related questions. The first one is
about accessing a variable from the caller function. Owing to the
differences in the scoping rules in S+ and R, it is not (at least
directly) possible to access f()'s variable "data" from g() in the
following example:
f <- function (...) {
data <- my.readfile(...);
g(...)
}
g <- function (...) {
# Do something with data?
}
The thing is that passing "data" as an argument to g() involves
copying
the data, if I understood correctly. Something I'd be keen to avoid
because in the real programme I want to write, g() is called many a time
and data is rather big (not infamously massive, though, something like a
500x20 matrix). If no other solution exists, I can do this:
f <- function (...) {
data <- my.readfile(...);
g <- function (...) {
# Do something with data
}
g(...)
}
This may be very common practice in R, I don't know, but my feeling as a
beginner is that it's rather inelegant, especially if you need define
many such functions. So my first question is: is there another way of
sharing a variable across functions or should I consider that the
elegance isn't an issue?
The second question relates to modifying a variable from within a
function. In the real code, this applies to another variable, but let's
suppose that within g(), I'd like to modify data[index] for a given
index. Apparently, data[index] <- new.value makes data become a local
variable of g and any modification remains unnoticed by f() and other
functions. So, is there any convenient to do that without returning big
arrays, vectors, or whatever?
Many thanks in advance.
--
Joss
