Bar charts

Bar charts are usually used to explore how one (or more) categorical variables are distributed. In qplot(), this is done using the geom option bar. This geometry counts the number of occurrences of each factor variable, which appears in the data. To show an example of the bar chart, we will use the movies dataset, which is included within the ggplot2 package. We have already seen how to recall the dataset included with the basic installation of R, but if you are interested in the list of datasets within a specific package (ggplot2 in this case), you can use the following code:

require(ggplot2)       ## Load ggplot2 if needed
data(package="ggplot2")  ## List of dataset within ggplot2

The movies dataset contains information about movies, including the rating, from the http://imdb.com/ website. You can get a more detailed description in the help page of the dataset.

This dataset contains different variables but, for our example, we will not need all of them, so let´...