Learning Statistics with R - A tutorial for psychology students and other beginners, 2018a

dan.grump
40 50 60 70 80 90
5 6 7 8 9
dan.sleep
Figure 6.17: A fancy scatterplot drawn using the scatterplot() function in the car package.
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+ smooth = FALSE
+ )
The first two arguments should be familiar: the first input is a formula (dan.grump ~ dan.sleep) telling
R what variables to plot, 15 and the second specifies a data frame. The third argument smooth I’ve set
to FALSE to stop the scatterplot() function from drawing a fancy “smoothed” trendline (since it’s a bit
confusing to beginners). The scatterplot itself is shown in Figure 6.17. As you can see, it’s not only
drawn the scatterplot, but its also drawn boxplots for each of the two variables, as well as a simple line
of best fit showing the relationship between the two variables.
6.6.1 More elaborate options
Often you find yourself wanting to look at the relationships between several variables at once. One
useful tool for doing so is to produce a scatterplot matrix, analogous to the correlation matrix.
15 You might be wondering why I haven’t specified the argument name for the formula. The reason is that there’s a bug
in how the scatterplot() function is written: under the hood there’s one function that expects the argument to be named
x and another one that expects it to be called formula. I don’t know why the function was written this way, but it’s not an
isolated problem: this particular kind of bug repeats itself in a couple of other functions (you’ll see it again in Chapter 13).
The solution in such cases is to omit the argument name: that way, one function “thinks” that you’ve specified x and the
other one “thinks” you’ve specified formula and everything works the way it’s supposed to. It’s not a great state of affairs,
I’ll admit, but it sort of works.
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