The Art of R Programming

Environment and Scope Issues

A function—formally referred to as a closure in the R documentation—consists not only of its arguments and body but also of its environment. The latter is made up of the collection of objects present at the time the function is created. An understanding of how environments work in R is essential for writing effective R functions.

The Top-Level Environment

Consider this example:

> w <- 12
> f <- function(y) {
+    d <- 8
+    h <- function() {
+       return(d*(w+y))
+    }
+    return(h())
+ }
> environment(f)
<environment: R_GlobalEnv>

Here, the function f() is created at the top level—that is, at the interpreter command prompt—and thus has the top-level environment, which in R output is referred to as R_GlobalEnv but which confusingly ...