Miscellaneous Graphs - R Graphics - page 362

Discussion
To better convey useful information, you may want to customize the appearance of the heat map.
With this example, we'll reverse the y-axis so that it progresses from top to bottom, and we'll add
tick marks every four years along the x-axis, to correspond with each presidential term. We'll
also change the color scale using scale_fill_gradient2() , which lets you specify a midpoint
color and the two colors at the low and high ends ( Figure 13-13 ):
p + geom_tile() +
scale_x_continuous(breaks = seq( 1940 , 1976 , by = 4 )) +
scale_y_reverse() +
scale_fill_gradient2(midpoint = 50 , mid = "grey70" , limits = c( 0 , 100 ))
Figure 13-13. A heat map with customized appearance
See Also
If you want to use a different color palette, see Using a Manually Deined Palette for a Continu-
ous Variable .
Creating a Three-Dimensional Scatter Plot
Problem
You want to create a three-dimensional (3D) scatter plot.
Solution
We'll use the rgl package, which provides an interface to the OpenGL graphics library for 3D
graphics. To create a 3D scatter plot, as in Figure 13-14 , use plot3d() and pass in a data frame
where the first three columns represent x, y, and zcoordinates, or pass in three vectors repres-
enting the x, y, and zcoordinates.