How to create Boxplots in R
Refs:
http://en.wikipedia.org/wiki/Boxplot
http://www.r-project.org/
Suppose you have data such as:
number_of_threads thread time
1 1 10
2 1 20.5
2 2 19.5
3 1 30
3 2 25
3 3 35
This table represents made up data describing some system testing, where the system is exercised with 1,2,3... concurrent users. You want to produce a boxplot showing the timings for each number of concurrent users. Here's the magic incantation in R:
Assuming the above file is saved to data.txt
1) Use R's Misc menu to change to the correct working directory
2) Load the data into a dataframe with
myresults = read.table("data.txt", header=TRUE)
3) Generate the boxplot with
boxplot( time ~ number_of_threads, myresults)
To jazz it up with some axis labels:
boxplot( time ~ number_of_threads, myresults, xlab="Concurrent users", ylab="time")
Adding several boxplots on the same axis:
boxplot( time ~ number_of_threads, myresults, add=TRUE)
*Warning* - if you don't see your new boxplot, then it's because for some nutty reason the plot doesn't automatically rescale, and you need to set the scale explicitly with ylim=c(0,40) or similar.
Making the boxes a particular colour:
boxplot( time ~ number_of_threads, myresults, col="yellow")
and adding a legend:
legend(2,9m c("plot1","plot2"), fill=c("red","yellow"))
