Creating a facet box plot

With faceting tools at hand, we will now give the car::Salaries data frame a better look. There are many aspects of this particular data set that stood out in the analysis made at previous chapters. In this recipe, a facet box plot will be crafted. We shall use ranks and discipline variables to create facets. Variables sex and salary are going to fit respectively the x and y axes.

Variable discipline is assigned with A for theoretical departments and B for applied ones, so this recipe will also teach how to relabel these in order to make it intuitive.

How to do it...

Let us now create a facet box plot:

1. Store data into a new object and factor discipline properly:

> library(car)
> data_box <- Salaries
> data_box$discipline <- factor(data_box$discipline, labels = c('theoretical','applied'))

2. Craft a box plot and call facet_grid():

> library(ggplot2)
> boxplot <- ggplot(data = data_box) + 
   geom_boxplot(aes( x = sex, y = salary), position = 'identity...