How do you use a function you have made to calculate the % effect on the output of changing the input by 1%?

If the function is nonlinear, there should be a starting value that the percentage is calculated from.

x <- -2
get_y <- function(x) {
  y <- xˆ2
}
get_z <- function(x) {
  z <- get_y(x) * x
}
get_result <- function(x) {
  get_z(x)
}

I want to get a value that indicates what happens to z in % if we change x from -2 by 1%.

What do I need to do with get_result(x) to get that?

Bonus: how would I create a dataframe of x and z values from these?

This should work. Each function needs to return something, and the get_result function should return how much z changes if you change x by pct_change

get_y <- function(x) {
  x ^ 2
}

get_z <- function(x) {
  get_y(x) * x
}
get_result <- function(x, pct_change = 0.01) {
  z_orig <- get_z(x)
  z_new <- get_z((1 + pct_change)*x)
  
  (z_new - z_orig)/z_orig
  
}

get_result_df <- function(x, pct_change){
  
  data.frame(x = x,
             z = get_z(x),
             x_pct_change = pct_change,
             z_pct_change = get_result(x, pct_change))
  
}

Here's an example:

get_result_df(x = -2, pct_change = 0.01)
#    x  z x_pct_change z_pct_change
# 1 -2 -8         0.01     0.030301