R: Data Analysis and Visualization

Visualization methods

We are now going to see how we can create these kinds of visualizations on our own.

Categorical and continuous variables

We have seen that box plots are a great way of comparing the distribution of a continuous variable across different categories. As you might expect, box plots are very easy to produce using ggplot2. The following snippet produces the box-and-whisker plot that we saw earlier, depicting the relationship between the petal lengths of the different iris species in the iris dataset:

  > library(ggplot)
  > qplot(Species, Petal.Length, data=iris, geom="boxplot", 
  +       fill=Species)

First, we specify the variable on the x-axis (the iris species) and then the continuous variable on the y-axis (the petal length). Finally, we ...