Labelling Horizontal Line in ggplot2 Graphic in R (Example Code)

In this R tutorial you’ll learn how to draw a straight labeled line in a ggplot2 plot.

Setting up the Example

data(iris)                     # Loading iris data
head(iris)
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa
install.packages("ggplot2")    # Install & load ggplot2
library("ggplot2")
my_plot <- ggplot(iris,        # ggplot2 Plot without horizontal line
                  aes(x = Sepal.Length,
                      y = Sepal.Width)) +
  geom_line()
my_plot

r graph figure 1 labelling horizontal line ggplot2 graphic r

Example: Draw Horizontal Line with Label to ggplot2 Graphic

my_plot +                      # Adding horizontal line & label
  geom_hline(aes(yintercept = 3.15), col = "red") +
  geom_text(aes(min(Sepal.Length),
                3.15,
                label = 3.15,
                vjust = - 1),
            col = "red")

r graph figure 2 labelling horizontal line ggplot2 graphic r

Related Articles

Have a look at the following R programming tutorials. They focus on topics such as graphics in R, ggplot2, and text elements:

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