Introduction to Statistics (MAT/SST 115.03 2008S)

Dot Plots


Quick Example

library(BHH2, lib="/home/rebelsky/Stats115/Packages")
dotPlot(vector, 
  axes=FALSE,
  main="Title"
  xlab="Label of X Axis"
)
axis(1, seq(from=min,to=max,by=step))

Some Notes

Although Workshop Statistics makes a lot of use of dot plots, those kinds of dot plots are not standard in R. Why not? Because there are other ways to represent data, such as histograms, that are often more useful. So why does Workshop Statistics use these simple dot plots? Because they're easy to construct by hand.

Fortunately, R is extensible. Hence, some folks who decided that they needed simple dot plots added support for them in R. However, you need to load the BHH2 package, which adds the dotPlot command.

If you're working at home, on your own computer, you can probably add the package with the following commands:

If you're working at home, on your own computer, you can probably add the package with the following commands:

install.packages("BHH2")
library(BHH2)

When you enter the first command, R will probably ask you where to look for R packages. We generally use the Iowa State server, which appears in most lists as “USA (Iowa)”.

Unfortunately, our Linux computers are not configured to allow you to extend R. Hence, you need a somewhat different command.

library(BHH2, lib="/home/rebelsky/Stats115/Packages")

Once you've loaded this library, the dotPlot command is available to you.

As in the case of barplot, you can call dotPlot with just the data you want plotted. (In this case, you don't have to turn it in to a table first.)

dotPlot(vector)

Of course, you'll want to add a title to the figure. As in almost every case, you can use the main option to add titles.

You can add a label to the X axis with the xlab=... option.

You may also notice that the tick marks on the X axes are somewhat awkward. Unfortunately, it's not nearly so easy to fix those. The solution is to draw the dotplot without any axes and then to add them back in. You tell R not to draw axes by adding axes=FALSE to the command. You tell R what ticks to use when drawing a horizontal axis with axis(1,vector), where the vector has the tick marks.

dotPlot(Survey$States, 
  axes=FALSE,
  main="States visited by Intro Stats Students", 
  xlab="Number of States"
)
axis(1, seq(from=0,to=50,by=5))

Creative Commons License

Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright (c) 2007-8 Samuel A. Rebelsky.

This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.