Question

I have the following function:

s_c <- function(n, t){
    r_num <- runif(1,min=0,max=1)
    use <- sample(s[,1],1)
    use2 <- subset(s,s[,1]==use,2)
    use2 <- as.numeric(use2)
    ne_s <- sample(subset(s,s[,2]!=use2,2),1)

    Return(use) 
    if (t>50 & r_num<0.5){
        ne_s
    }
        else 
           0  
}

I would actually like to use the variable created in the function in a command outside the function, so I would like to “return” in the sense of being able to refer to the variable outside the function

Question 2:

What if I would like to do an assignment within the if statement, for example

 if (t>50 & r_num<0.5){
        s[,4]=use
    }

Can this be done?

Answer 1

Although you should probably return the two values as a list, you can affect the parent’s environment quite easily.

Replace this:

Return(use)

with this:

use <<- use

For your edit, you could use the syntax:

s[,4] <<- use

Note: The “parent’s environment” is NOT the environment in which the function is called. It is the environment in which the function is defined. It is for this reason that a function in R is known as a closure. Explicitly:

s_c <- function() {
  use <<- 1
}

f <- function() {
  use <- 0
  s_c()
  return(use)
}

f() will return 0. s_c() is modifying a different use variable (in a different environment).