Legends - R Graphics - page 311

using theme() ( Figure 10-17 , right). To do this, you will need to specify the height using the
unit() function from the grid package:
library(grid)
p + scale_fill_discrete(labels = c( "Control" , "Type 1\ntreatment" ,
"Type 2\ntreatment" )) +
theme(legend.text = element_text(lineheight = .8 ),
legend.key.height = unit( 1 , "cm" ))