This section introduces the functionality of the base-R function boxplot. Note that for some data formats, the plot function with x being a factor variable will also work.
The function boxplot2()[in gplots package] can be used to create a box plot annotated with the number of observations.
Install gplots:
install.packages("gplots")
Use boxplot2() [in gplots]:
library("gplots") # Box plot with annotation boxplot2(len ~ dose, data = ToothGrowth, frame = FALSE)
# Put the annotation at the top boxplot2(len ~ dose, data = ToothGrowth, frame = FALSE, top = TRUE)