Why does rm inside a function not delete objects?

Question

rel.mem <- function(nm) {
  rm(nm)
}

I defined the above function rel.mem -- takes a single argument and passes it to rm

> ls         


        

Answer 1

The quick answer is that you're in a different environment - essentially picture the variables in a box: you have a box for the function and one for the Global Environment. You just need to tell rm where to find that box.

So

rel_mem <- function(nm) {
   # State the environment
   rm(list=nm, envir = .GlobalEnv )
}
x = 10
rel_mem("x")

Alternatively, you can use the pos argument, e.g.

rel_mem <- function(nm) {
   rm(list=nm, pos=1 )
}

If you type search() you will see a vector of environments, the global is number 1.

Another two options are

• envir = parent.frame() if you want to go one level up the call stack
• Use inherits = TRUE to go up the call stack until you find something

---

In the above code, notice that I'm passing the object as a character - I'm passing the "x" not x. We can be clever and avoid this using the substitute function

rel_mem <- function(nm) {
   rm(list = as.character(substitute(nm)), envir = .GlobalEnv )
}

To finish I'll just add that deleting things in the .GlobalEnv from a function is generally a bad idea.

Further resources:

• Environments:http://adv-r.had.co.nz/Environments.html
• Substitute function: http://adv-r.had.co.nz/Computing-on-the-language.html#capturing-expressions

Answer 2

If you are using another function to find the global objects within your function such as ls(), you must state the environment in it explicitly too:

rel_mem <- function(nm) {
   # State the environment in both functions
   rm(list = ls(envir = .GlobalEnv) %>% .[startsWith(., "plot_")], envir = .GlobalEnv)
}