Returning from a sub function

[gordon]

I'm trying to write a function which will cause its parent function to return a value. Here is the reprex:

test <- function(data) {
  val <- checkForValue(data)
  if (!isFALSE(val)) {
    return(val)
  }
  return("bar")
}

checkForValue <- function(data) {
  if ("test" %in% names(data)) {
    return(data[["test"]])
  }
  return(FALSE)
}

mtcars$test <- "foo"
test(mtcars)

This all works, but I'd like to have checkForValue cause test to return directly rather than doing the if/else dance

[pieterjanvc]

Hi,

I might be missing something, but I think this will suffice:

test <- function(data){
  if ("test" %in% names(data)) {
    return(data[["test"]])
  }
  return("bar")
}

mtcars$test <- "foo"
test(mtcars)

Hope this helps,
PJ

[gordon]

Oh yes, but in this case I actually want the sub function, the idea is to write a sub function that does that return and allows me to call it in a bunch of other functions.

[brycemecum]

Hey @gordon, interesting question.

To my knowledge, you can't do exactly what you're asking (cause one function to return from another's body). But your code above is effectively doing that when the inner function returns a value that causes an early return of the outer function. I see and write code similar to this all the time.

Thanks for producing the reprex, but I wonder if sharing an example that more closely resembles the code you're working on my help clarify things?

[gordon]

I figured it out!

test <- function(data) {
  eval(checkForValue(data))
  return("bar")
}

checkForValue <- function(data) {
  if ("test" %in% names(data)) {
    assign("return_data", data[["test"]], parent.frame())
    out <- rlang::expr(print(return_data))
    return(out)
  }
}

[technocrat]

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