A common way of describing univariate data is with a frequency distribution. We've already seen an example of a frequency distribution when we looked at the preferences for soy ice cream at the end of the last chapter. For each flavor of ice cream (categorical variable), it depicted the count or frequency of the occurrences in the underlying data set.
To demonstrate examples of other frequency distributions, we need to find some data. Fortunately, for the convenience of useRs everywhere, R comes preloaded with almost one hundred datasets. You can view a full list if you execute help (package="datasets"). There are also hundreds more available from add on packages.
The first data set that we are going to use is mtcars—data on the design and performance of 32 automobiles that was extracted from the 1974 Motor Trend US magazine. (To find out more information about this dataset, execute ?mtcars.)
Take a look at the first few lines of this dataset using the head function...