#activate the package
library(ggplot2)

#load the dataframe
ID <- 1:400
values <- c(rnorm(200, mean=50, sd=22), rnorm(200, mean=20, sd=10))
class <- c(rep("first", 200), rep("second",200))
my.dataframe <- data.frame(ID, values, class)

#jitter plot 
ggplot(my.dataframe, aes(class, values)) + 
  geom_jitter()


#jitter plot narrow
ggplot(my.dataframe, aes(class, values)) + 
  geom_jitter(width=.1)

#jitter plot too narrow
ggplot(my.dataframe, aes(class, values)) + 
  geom_jitter(width=.01)

#point plot
ggplot(my.dataframe, aes(class, values)) + 
  geom_point()

#jitter plot with qplot)()
qplot(class, values, data=my.dataframe, geom="jitter")