How to dynamically reference datasets in function call of linear regression - r

Question

Let's say I have a function like this:
data("mtcars")
ncol(mtcars)
test <- function(string){
fit <- lm(mpg ~ cyl,
data = string)
return(fit)
}
I'd like to be able to have the "string" variable evaluated as the dataset for a linear regression like so:
test("mtcars")
However, I get an error:
Error in eval(predvars, data, env) : invalid 'envir' argument of
type 'character'
I've tried using combinations of eval and parse, but to no avail. Any ideas?

Answer 1

You can use get() to search by name for an object.
test <- function(string){
fit <- lm(mpg ~ cyl, data = get(string))
return(fit)
}
test("mtcars")
# Call:
# lm(formula = mpg ~ cyl, data = get(string))
#
# Coefficients:
# (Intercept) cyl
# 37.885 -2.876
You can add one more line to make the output look better. Notice the change of the Call part in the output. It turns from data = get(string) to data = mtcars.
test <- function(string){
fit <- lm(mpg ~ cyl, data = get(string))
fit$call$data <- as.name(string)
return(fit)
}
test("mtcars")
# Call:
# lm(formula = mpg ~ cyl, data = mtcars)
#
# Coefficients:
# (Intercept) cyl
# 37.885 -2.876

Answer 2

Try this slight change to your code:
#Code
test <- function(string){
fit <- lm(mpg ~ cyl,
data = eval(parse(text=string)))
return(fit)
}
#Apply
test("mtcars")
Output:
Call:
lm(formula = mpg ~ cyl, data = eval(parse(text = string)))
Coefficients:
(Intercept) cyl
37.885 -2.876