How to pass on the name of a variable in R

Question

So, I'm making a function like

    example <- function(x, y){
z <- data.frame("variable name" = y, "Quantity of 1" = sum(x==1, na.rm = TRUE))
eval(as.character(y)) <<- z
}

list <- sample(c(0,1), size = 12, replace = TRUE)

If I evaluate my function using

example(list, "list")

It gives me an

error in eval(as.character(y)) <<- z: object 'y' not found

I want the function to give me a variable which I could find by the name I pass on it (as "Y") given that I'll have to work using the same procedures multiples times.

Answer 1

I think you are looking for assign:

example <- function(x, y){
  z <- data.frame("variable name" = y, "Quantity of 1" = sum(x==1, na.rm = TRUE))
  assign(y, z, envir = parent.frame())
}

list <- sample(c(0,1), size = 12, replace = TRUE)

example(list, "list")

list
#>   variable.name Quantity.of.1
#> 1          list             5

However, please note that this is not a great idea. You should try to avoid writing functions that can over-write objects in the global environment (or other calling frame) as this can have unintended consequences and is not idiomatic R.

It would be better to have:

example <- function(x, y){
  data.frame("variable name" = y, "Quantity of 1" = sum(x==1, na.rm = TRUE))
}

and do

list <- example(list, "list")

or, better yet:

example <- function(x){
  data.frame("variable name" = deparse(substitute(x)), 
             "Quantity of 1" = sum(x==1, na.rm = TRUE))
}

So you can just do:

list <- example(list)

Furthermore, it is a good idea to avoid using a common function name like list as a variable name.