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

In function argument col is evaluated before using in function with (that opposite to interactive use). Here you have two solutions to this problem.

foo1 <- function(obj, col) {
          with(obj, print(eval(col)))
        }
foo1(mydf, quote(a))# here you have to remember to quote argument


foo2 <- function(obj, col) {
          col <- as.expression(as.name(substitute(col)))#corrected after DWIN comment
          with(obj, print(eval(col)))
        }
foo2(mydf, a)# this function does all necessary stuff