The lattice package is a useful package to learn, especially for analysts who like to work in formula notation (y~x).
In this example, we will run a lattice plot in order to plot Not.Covered.Pct on the y-axis, Year on the x-axis, and produce separate plots by category.
The main call is specified by the following:
xyplot(Not.Covered.Pct ~ Year | cat, data = x3)
Since we are plotting the top 10 groups, we can specify layout=c(5,2) to indicate we want to arrange the 10 plots in a 5*2 matrix. Not.Covered.Pct is to be arranged on the y axis (left side of the ~ sign), and Year is arranged along the x-axis (right side of ~ sign). The bar (|) indicates that the data is to be plotted separately by each category: