Using ellipsis parameters alongside other parameters-CodePudding

I want to use a function to modify a plot based on the parameters passed. However, I'm not sure what format I should convert the list of modifications parameters into, to be used as parameters within the respective 'geom'.

library(ggplot2)

data <- tibble(a = 1:3, b = 11:13)

p <- ggplot(data)

plot_modify <- function(p, geom = "", ...){
  modifications <- list(...)
  if(geom == "point"){
    p <- p   geom_point(aes(x = a, y = b), modifications)
  }
  return(p)
}

plot_modify(p, "point", alpha=0.1, size = 0.3)

P.s. I intend to validate the list of parameters based on each 'geom' later on.

CodePudding user response：

After you capture the values in the ellipse, you are responsible for passing them along. In order to inject those values into subsequent calls, you'll need to build the call using something like do.call using base R methods

plot_modify <- function(p, geom = "", ...){
  modifications <- list(...)
  if(geom == "point"){
    p <- p   do.call("geom_point", c(list(aes(x = a, y = b)), modifications))
  }
  return(p)
}

But do note that list(...) will force evaluation of all your parameters which is slightly different than how the function behaves normally.

If you wanted to use more of an rlang strategy you can do

plot_modify <- function(p, geom = "", ...){
  modifications <- list(...)
  if(geom == "point"){
    p <- p   rlang::inject(geom_point(aes(x = a, y = b), !!!modifications))
  }
  return(p)
}