passing parameters to ggplot

Question

would like to create a function that generates graphs using ggplot. For the sake of simplicity, the typical graph may be

ggplot(car, aes(x=speed, y=dist)) + geom_point()

The function I would like to create is of the type

f <- function(DS, x, y) ggplot(DS, aes(x=x, y=y)) + geom_point()

This however won't work, since x and y are not strings. This problem has been noted in previous SO questions (e.g., this one), but without providing, in my view, a satisfactory answer. How would one modify the function above to make it work with arbitrary data frames?

user_5193830 · Answer

One approach that I can think of is using match.call() to reach the variable names contained by the parameters/arguments passed to the custom plotting function and then use eval() on them. In this way you avoid passing them as quoted to your custom function, if you do not like that.

library(ggplot2)

fun <- function(df, x, y) {
    arg <- match.call()
    ggplot(df, aes(x = eval(arg$x), y = eval(arg$y))) + geom_point()
} 
fun(mpg, cty, hwy) # no need to pass the variables (column names) as quoted / as strings

passing parameters to ggplot

4 Answers