CODEWITHSUNDEEP
r
momeara
momeara

Reputation: 1381

R execute function as if it were entered in an interactive session

if I have a function in R

f <- function(){
    x <- 3
}

then when I execute the function in an interactive session, like this

> f()
>

the variable x is not defined/accessible

> x
Error: object 'x' not found
>

Is there a way to execute f as if the contents of the function were entered line by line into the interactive session?

EDIT: Here is the reason why I would like this functionality. I have a collection of scripts that I use to semi-automate a multi-step analysis workflow. To use them, I usually source a scripts and it initializes a session with pre-processed data. Then I can interactively continue the analysis from there.

In order to attach meta-data to the scripts, I have wrapped the analysis scripts as S4 objects implementing a base class. Currently I have the contents of each script in a member function called run() that can be executed. The issue is that while I can execute the run() function to preform the initial analysis computation, it cannot setup the environment with the pre-processed data.

Upvotes: 2

Views: 839

Answers (1)

Tommy
Tommy

Reputation: 40813

No, I don't believe that it is possible. UPDATE Well, I now believe it is possible. See below.

When the function f is executed, a local environment is created that initially has the parameter values (none in your case). The assignment to x happens in that local environment.

If you modify f you can achieve what you want though. Here are a couple of alternatives:

# Simply return the value:
f <- function() {
   x <- 3 
   x # returns x. return(x) also works fine.
}
f() # returns 3

# Assign to global env
f <- function() {
  x <<- 3 # Assigns in global env - but see help("<<-") for details
}
f()
x # 3

# Return the local environment
f <- function(foo=13) {
  x <- 3 # local assignment
  environment() # return the local environment
}

e <- f()
e$x # 3
e$foo # 13

Note that your original version of f also returned 3, but invisibly - the default result from an assignment is an invisible value. There is also a special function, invisible for that:

f <- function(){
  x <- 3
}

print( f() ) # 3
a <- f() 
a # 3

invisible(42) # won't show...
print( invisible(42) ) # ...but it's there!

UPDATE Thinking about it a bit more, of course it is possible. Let's make a slightly more interesting function:

f <- function(a, b) {
  cat("I got",a,"and",b,"\n")
  x <- a+b
}

# Ensure there is no x to prove that the following works...
rm(x)

# First assign the input parameters to f.
a <- 5
b <- 3

# Then evaluate the body.
eval(body(f))
x # 8

Upvotes: 3

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