What is the difference between assign() and <<- in R?

Question

The normal approach to writing functions in R (as I understand) is to avoid side-effects and return a value from a function.

contained <- function(x) {
          


        

Answer 1

As pointed out by @John in his answer, assign lets you specify the environment specifically. A specific application would be in the following:

testfn <- function(x){

    x_squared <- NULL

    escape <- function(x){
        x_squared  <<- x^2
        assign("x_times_x", x*x, envir = parent.frame(n = 1))
    }

    escape(x)

    print(x_squared)
    print(x_times_x)
}

where we use both <<- and assign. Notice that if you want to use <<- to assign to the environment of the top level function, you need to declare/initialise the variable. However, with assign you can use parent.frame(1) to specify the encapsulating environment.