How to use with/within inside a function?

Question

I\'m struggling to understand why does this doesn\'t work.

df <- data.frame(a=1:10, b=1:10)

foo <- function(obj, col) {
   with(obj, ls())
   with(obj         


        

Answer 1

Anything that is passed to a function must be an object, a string or a number. There are two problems with this:

1. In this case you're trying to pass "a" as an object, when you should really be passing it like a string.
2. with(obj, ls())) will return to the functions environment (function scoping) and not the screen unless you tell it to print.

What you want is more like:

foo <- function(obj, col) {
       print(with(obj, ls()))
       with(obj, print(obj[[col]]))
    }

foo(df, "a")

Or if you're only looking for the one column to be printed:

foo <- function(obj, col) {
           with(obj, print(obj[[col]]))
        }

foo(df, "a")