#activate the package
library(ggplot2)

#load the dataframe
ID <- 1:60
values <- c(rnorm(20, mean=50, sd=22), rnorm(20, mean=20, sd=10), rnorm(20, mean=35, sd=5))
class <- c(rep("first", 20), rep("second",20), rep("third",20))
my.dataframe <- data.frame(ID, values, class)

#boxplot with 2 categories
ggplot(my.dataframe, aes(class,values)) + 
  geom_point()

qplot(class, values, data=my.dataframe, geom=("point"))