You want to plot a function.

Use stat_function(). It’s also necessary to give ggplot() a dummy data frame so that it will get the proper x range. In this example we’ll use dnorm(), which gives the density of the normal distribution (Figure 13-4, left):

# The data frame is only used for setting the range
p <- ggplot(data.frame(x=c(-3,3)), aes(x=x))

p + stat_function(fun = dnorm)

Figure 13-4. Left: the normal distribution; right: the t-distribution with df=2

Some functions take additional arguments. For example, dt(), the function for the density of the t-distribution, takes a parameter for degrees of freedom (Figure 13-4, right). These additional arguments can be passed to the function by putting them in a list and giving the list to args: