In this chapter, we are going to describe relationships and begin working with multivariate data, which is a fancy way of saying samples containing more than one variable.
The troublemaker reader might remark that all the datasets that we've worked with thus far (mtcars and airquality) have contained more than one variable. This is technically true but only technically. The fact of the matter is that we've only been working with one of the dataset's variables at any one time. Note that multivariate analytics is not the same as doing univariate analytics on more than one variable—multivariate analyses and describing relationships involve several variables at the same time.
To put this more concretely, in the last chapter we described the shape of, say, the temperature readings in the airquality dataset:
head(airquality)
Ozone Solar.R Wind Temp Month Day
1 41 190 7.4 67 5 1
2 36 118 8.0 72 5 2
3 12 149 12.6 74 5 3
4 18 ...