R Graphics Cookbook

Chapter 13. Miscellaneous Graphs

There are many, many ways of visualizing data, and sometimes things don’t fit into nice, tidy categories. This chapter shows how to make some of these other visualizations.

Making a Correlation Matrix

Problem

You want to make a graphical correlation matrix.

Solution

We’ll look at the mtcars data set:

mtcars

                      mpg cyl  disp  hp drat    wt  qsec vs am gear carb
 Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
 Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
 Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
 ...
 Ferrari Dino        19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6
 Maserati Bora       15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8
 Volvo 142E          21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2

First, generate the numerical correlation matrix using cor. This will generate correlation coefficients for each pair of columns:

mcor <- cor(mtcars)

# Print mcor and round to 2 digits
round(mcor, digits=2)

       mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
mpg   1.00 -0.85 -0.85 -0.78  0.68 -0.87  0.42  0.66  0.60  0.48 -0.55
cyl  -0.85  1.00  0.90  0.83 -0.70  0.78 -0.59 -0.81 -0.52 -0.49  0.53
disp -0.85  0.90  1.00  0.79 -0.71  0.89 -0.43 -0.71 -0.59 -0.56  0.39
hp   -0.78  0.83  0.79  1.00 -0.45  0.66 -0.71 -0.72 -0.24 -0.13  0.75
drat  0.68 -0.70 -0.71 -0.45  1.00 -0.71  0.09  0.44  0.71  0.70 -0.09
wt   -0.87  0.78  0.89  0.66 -0.71  1.00 -0.17 -0.55 -0.69 -0.58  0.43
qsec  0.42 -0.59 -0.43 -0.71  0.09 -0.17  1.00  0.74 -0.23 -0.21 -0.66
vs    0.66 -0.81 -0.71 -0.72  0.44 -0.55  0.74  1.00  0.17  0.21 -0.57
am    0.60 -0.52 -0.59 -0.24 ...