R: ggplot2 make two geom_tile plots have equal height

Question

I have two ggplot geom_tile plots that I put together using grid.arrange() from the gridExtra library. This is the result

library(ggplot2)
library(plyr)

p3         


        

Answer 1

p3b <- ggplot_build(p3)
p4b <- ggplot_build(p4)
g3 = ggplot_gtable(p3b) ; g4 = ggplot_gtable(p4b)

# work out the number of horizontal tiles
n3 <- length(p3b[["panel"]][["ranges"]][[1]][["x.major_source"]])
n4 <- length(p4b[["panel"]][["ranges"]][[1]][["x.major_source"]])

require(gtable)
require(grid)
g <- cbind(g3, g4, size = "first")
#adjust the panel widths in proportion to n4/n3
panels <- g$layout$l[grep("panel", g$layout$name)]
g$widths[panels] <- lapply(c(1,n4/n3), unit, "null")
grid.newpage()
grid.draw(g)