How to do it...

Let us get started with drawing bivariate dot plots using ggplot2:

1. Use geom_dotplot() to draw a simple box plot:

> library(ggplot2)
> box1 <- ggplot(car::Salaries, aes( x = rank, y = salary))
> box1 + geom_dotplot(binaxis = 'y', dotsize = .3, stackdir = 'center')

As result, we get the following figure:

Figure 3.3 Simple ggplot2 dotplot.

1. A third aspect can be visualized by picking aes(fill):

> box1 + geom_dotplot(binaxis = 'y', dotsize = .3, 
>                     stackdir = 'center', aes(fill = sex))

Following figure shows that sex can now be visualized as graphic:

Figure 3.4 Dot plot with colors attached.

There are now some nuts and bolts to go through.