How to plot functions in R

Problem

We would like to plot functions in R.

Solution

In our example we will plot the following quadratic equation: 2x² + 20x + 3 = 0

• Option 1: base package

f <- function(x) {
  x ^ 2 + 20 * x + 3
}
curve(expr = f, from = -100, to = 100)


• Option 2: ggplot2

library(ggplot2)
ggplot(data.frame(x = c(-100, 100)), aes(x)) +
  stat_function(
    fun = function(x) {
      x ^ 2 + 20 * x + 3
    }
  ) +
  geom_hline(yintercept = 0) +
  geom_vline(xintercept = 0)

 

Notes

If we want to add more functions:

• Option 1: Base package

f1 <- function(x) {
  x ^ 2 + 20 * x + 3
}
f2 <- function(x) {
  x ^ 2 + 50 * x + 100
}
curve(expr = f1, from = -100, to = 100)
curve(expr = f2, from = -100, to = 100, col  = 2, add = TRUE)


• Option 2: ggplot2

ggplot(data.frame(x = c(-100, 100)), aes(x)) +
  stat_function(
    fun = function(x) {
      x ^ 2 + 20 * x + 3
    }
  ) +
  stat_function(
    fun = function(x) {
      x ^ 2 + 50 * x + 100
    },
    colour = "red"
  ) +
  geom_hline(yintercept = 0) +
  geom_vline(xintercept = 0)
 

References

• ggplot2 reference