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Question

I'm using functions from an external package (that I cannot modify). These functions put a lot of stuff in the global environment, for instance the package does things like

the.data <<- data.frame(A=rnorm(10),B=rnorm(10),C=rnorm(10)) ## A sample dataset

package.plot <- function(){
  x.coords <<- the.data$A/the.data$B
  y.coords <<- the.data$C
  plot(x.coords, y.coords)
}

(obviously hyper-simplified example... here the key is that x.coods and y.coords are rather complex derivations, sufficiently complex that I do not want to recode them but find it advantageous to re-use the existing code)

I want to use these functions in my own scripts, namely make the same graph with ggplot. Of course, a first, obvious solution is

my.better.plot <- function(){
  package.plot()
  tibble(x.coords,y.coords) %>% ggplot(aes(x=x.coords,y=y.coords))+geom_point() # etc. 
}

However, this has two issues:

1. I end up plotting twice (a minor issue, it is sufficiently fast to be unnoticeable);
2. I "pollute" the global environment with global x.coords and y.coords

Hence, I would like to run package.plot() in a "pseudo-global" environment to avoid ending up with global variables that may be modified in an "uncontrolled" way.

A workaround, of course, is

my.better.plot <- function(){
  package.plot()
  tibble(x.coords,y.coords) %>% ggplot(aes(x=x.coords,y=y.coords))+geom_point() # etc. 
  rm(x.coords,envir=.GlobalEnv)
}

However, I'd prefer to do something like

my.better.and.cleaner.plot(){
  within.envir(dummy_env,my.better.plot)
}

.. assuming that there is, indeed, a function "within.envir" that allows to run its second argument in a mock global environment.

Is something like this possible at all? I did read http://adv-r.had.co.nz/Environments.html , but could not find the answer... (not one that I understood, at any rate). Bonus question: if this is possible, how can I extract the return value of ggplot from dummy_env and return it?

Answer 1

So this is unfortunately very hacky, since the <<- operator will traverse the environment tree upwards if it does not find the variable name (hence why you should basically never use it. The one workaround is to call the function from another environment that already has the variables in question initialized. Then it will assign it into those variables and not traverse further up into the globalEnv. You need to know the variable names beforehand though.

f <- function(x) a <<- x
f(5)
# a = 5 in GlobalEnv
rm(a)
CapturedCall <- function(fun, CapturedVars,...)
{
  stopifnot(is.function(fun))
  SandBox <- new.env()
  for(varName in CapturedVars) assign(varName, NA,SandBox)
  environment(fun) <- SandBox
  fun(...)
}

CapturedCall(f,"a",1)
#Nothing in GlobalEnv

Answer 2

This function avoids the side effects as much as possible:

  library(ggplot2)
  library(magrittr)
  library(tibble)
  my.better.plot <- function(){
    x.coords <- 1
    y.coords <- 1
    environment(package.plot) <- environment()
    
    bmp(tempfile())
    package.plot()
    dev.off()
    
    print(tibble(x.coords,y.coords) %>% ggplot(aes(x=x.coords,y=y.coords))+geom_point()) # etc. 
  }
  
  my.better.plot()
  #creates only the ggplot in the current device

  ls(globalenv())
  #[1] "my.better.plot" "package.plot"   "the.data"