R passes arguments by value

The title gives it away already: R passes arguments by value. What does this mean? Simply put, it means that an R function cannot change the variable that you input to that function. Let's look at a simple example (try it in the console):

triple <- function(x) {
  x <- 3*x
  x
}
a <- 5
triple(a)
a

Inside the triple() function, the argument x gets overwritten with its value times three. Afterwards this new x is returned. If you call this function with a variable a set equal to 5, you obtain 15. But did the value of a change? If R were to pass a to triple() by reference, the override of the x inside the function would ripple through to the variable a, outside the function. However, R passes by value, so the R objects you pass to a function can never change unless you do an explicit assignment. a remains equal to 5, even after calling triple(a).

Can you tell which one of the following statements is false about the following piece of code?

increment <- function(x, inc = 1) {
  x <- x + inc
  x
}
count <- 5
a <- increment(count, 2)
b <- increment(count)
count <- increment(count, 2)

Possible Answers

a and b equal 7 and 6 respectively after executing this code block.
After the first call of increment(), where a is defined, a equals 7 and count equals 5.
In the end, count will equal 10.
In the last expression, the value of count was actually changed because of the explicit assignment.

Exercise

R passes arguments by value

Instructions

Possible Answers