How to check if a variable exists in/assign a variable to a specific function's environment in R?

Question

I have two functions, "assign_fun" and "check_fun." I am trying to use "assign_fun" to check if a variable exists in "check_fun." If it doesn't exist, then I'd like to create that variable in the "check_fun" environment, NOT the global environment.

I understand the exists() and assign() functions have an "environment" argument...but not sure what to put in there. Here is my code:

assign_fun <- function() {
  
  #check if "e" exists in the environment of "check_fun"
  if (exists(x = "e")) {
    
    print(e)
    
  } else {
    
    #If "e" DOESNT exist in the environment of "check_fun", then assign it to that environment
    assign(x = "e", value = 5)
    print("assigned")
    
    }
}
  

check_fun <- function() {
  
  for (i in 1:5) {
    
    assign_fun()
    
  }
 output <- e
 print(output)
}

Since "assign_fun" is within "check_fun", I think I basically just have to go up one compartment "level" to check and assign.

ThomasIsCoding · Accepted Answer · 2021-01-20 00:40:26Z

1

If you want to put the assigned variable to the environment of caller function, you can use pos = sys.frame(-1) within assign, e.g.,

assign(x = "e", value = 5, pos = sys.frame(-1))

edited Jan 20, 2021 at 0:40

answered Jan 19, 2021 at 23:31

ThomasIsCoding

106k9 gold badges38 silver badges110 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Nova Over a year ago

Thank you for answer. Unfortunately, I specifically mentioned that I want "assign_test" to create the variable in the environment of "exists_test" and NOT the global environment.

Nova Over a year ago

Awesome. Does exists() have a similar "pos" argument?

ThomasIsCoding Over a year ago

@Nova Maybe where = ...? I am not sure

Nova · Accepted Answer · 2021-01-20 02:15:55Z

Turns out, the pos and where arguments work when the input is sys.frame(-1). This was a nice little educational exercise in environment compartmentalization.

The code now works with those changes:


assign_fun <- function() {
  
  #check if "e" exists in the environment of "check_fun"
  if (exists(x = "e", where = sys.frame(-1))) {
    
    print(get("e", pos = sys.frame(-1)))

  } else {
    
    #If "e" DOESNT exist in the environment of "check_fun", then assign it to that environment
    assign(x = "e", value = 5, pos = sys.frame(-1))
    print("assigned")
    
    }
}
  

check_fun <- function() {
  
  for (i in 1:5) {
    
    assign_fun()
    
  }
  output <- get("e")
  print("output")
  print(output)
}

check_fun()

Answer inspired by user: ThomasIsCoding

Collectives™ on Stack Overflow

How to check if a variable exists in/assign a variable to a specific function's environment in R?

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related