[SOLVED] NSE in nested function calls

NSE in nested function calls

I'd like to use a utility function to check whether a given column exists within a given data.frame. I'm piping within the tidyverse. The best I've come up with so far is

library(magrittr)

columnExists <- function(data, col) {
  tryCatch({
    rlang::as_label(rlang::enquo(col)) %in% names(data)
    },
    error=function(e) FALSE
  )
}

This works in the global environment

> mtcars %>% columnExists(mpg)
[1] TRUE
> mtcars %>% columnExists(bad)
[1] FALSE

But not when called from within another function, which is my actual use case

outerFunction <- function(d, col) {
  d %>% columnExists((col))
}
> mtcars %>% outerFunction(mpg)  # Expected TRUE
[1] FALSE
> mtcars %>% outerFunction(bad) # Expected FALSE
[1] FALSE

What am I doing wrong? Is it possible to have a single function that works correctly in the global environment and also when nested in another function?

I have found several SO posts related to checking for the existence of a given column or columns, but they all seem to assume either that the column name will be passed as a string or the call to check existence is not nested (or both). That is not the case here.

Solution

You want to pass though the original symbol in your outerFunction. Use

outerFunction <- function(d, col) {
  d %>% columnExists( {{col}} )
}

The "embrace" syntax will prevent early evaluation.