Annotate Count by Group to ggplot2 Boxplot in R (Example Code)

In this R programming post you’ll learn how to add the observations by group to a boxplot.

Preparing the Example

data(iris)                     # Example 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 ggplot2 package
library("ggplot2")             # Load ggplot2 package
my_plot <- ggplot(iris,        # Drawing ggplot2 boxplot without counts
                  aes(x = Species,
                      y = Petal.Width)) +
  geom_boxplot()
my_plot

r graph figure 1 annotate count group ggplot2 boxplot r

Example: Annotating Count Labels by Group to ggplot2 Boxplot

my_plot +                      # Annotating count labels to boxplot
  annotate("text",
           x = 1:length(table(iris$Species)),
           y = aggregate(Petal.Width ~ Species, iris, median)[ , 2],
           label = paste("n =", table(iris$Species)),
           size = 5,
           col = "purple",
           vjust = - 0.6)

r graph figure 2 annotate count group ggplot2 boxplot r

Further Resources & Related Tutorials

Please find some related R tutorials on topics such as colors, ggplot2, and groups in the following list.

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