Drawing functions in ggplot2 with geom_function

The geom_function can be used to draw functions in ggplot2. In this scenario you don’t need to pass a data frame to ggplot, but to specify the axis limits with xlim and the function to be plotted.

# install.packages("ggplot2")
library(ggplot2)

ggplot() +
xlim(c(0, 5)) +
geom_function(fun = cos)

Line customization

The function drawn can be customized with the typical arguments, such as color, lwd and linetype for the color, line width and line type, respectively.

# install.packages("ggplot2")
library(ggplot2)

ggplot() +
xlim(c(0, 5)) +
geom_function(fun = cos,
colour = "red",
lwd = 1,
linetype = 1)

stat_function

You can also use stat_function instead of geom_function. In this scenario you can change the default geom, as shown in the example below.

# install.packages("ggplot2")
library(ggplot2)

ggplot() +
xlim(c(0, 5)) +
stat_function(fun = cos,
geom = "point")

Additional arguments

Note that if the function you are plotting has additional arguments you can pass them through a list with the args argument. In the following example we are plotting a bessel function with besselJ, which requires an argument named nu.

# install.packages("ggplot2")
library(ggplot2)

ggplot() +
xlim(c(0, 50)) +
geom_function(fun = besselJ,
args = list(nu = 2))

Number of points

It should be noted that the number of points used to draw the function might not be enough, as in the previous example. To create a smoother function you can increase the value of the argument n.

# install.packages("ggplot2")
library(ggplot2)

ggplot() +
xlim(c(0, 50)) +
geom_function(fun = besselJ,
n = 400,
args = list(nu = 2))

Overlay over existing plot

If you have created a plot you can add a function over it with geom_function. The following example overlays the theoretical normal distribution over a normal distribution generated with 200 samples.

# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = x)) +
geom_density() +
geom_function(fun = dnorm, colour = "red")

Adding several functions

Finally, it is worth to mention that you can add several functions to the same plot, adding more layers.

# install.packages("ggplot2")
library(ggplot2)

ggplot() +
xlim(c(0, 50)) +
geom_function(fun = besselJ, n = 400,
aes(color = "BJ 0"),
args = list(nu = 0)) +
geom_function(fun = besselJ, n = 400,
aes(color = "BJ 2"),
args = list(nu = 2)) +
guides(colour = guide_legend(title = ""))

See also