How to set the height of the legend as well as the height of the plot plot?

Question

I placed two graphs: a line diagram on top and a heat map below.

I want the legend of the heat map to have the same height as the area of ​​the heat map plot, i.e. same length as y axis. I know that I can change the height and size of the legend using theme(legend.key.height = unit(...)) , but it will take a lot of trial and error before I find a suitable setting.

Is there a way to indicate the height of the legend so that it is exactly the same height as the area of ​​the heat map graph and would preserve this ratio when plotting in pdf?

A reproducible example with the code I tried:

 #Create some test data pp <- function (n, r = 4) { x <- seq(1:100) df <- expand.grid(x = x, y = 1:10) df$z <- df$x*df$y df } testD <- pp(20) #Define groups colbreaks <- seq(min(testD[ , 3]), max(testD[ , 3] + 1), length = 5) library(Hmisc) testD$group <- cut2(testD[ , 3], cuts = c(colbreaks)) detach(package:Hmisc, unload = TRUE) #Create data for the top plot testD_agg <- aggregate(.~ x, data=testD[ , c(1, 3)], FUN = sum) #Bottom plot (heatmap) library(ggplot2) library(gtable) p <- ggplot(testD, aes(x = x, y = y)) + geom_tile(aes(fill = group)) + scale_fill_manual(values = c("red", "orange", "yellow", "lightgreen")) + coord_cartesian(xlim = c(0, 100), ylim = c(0.5, 10.5)) + theme_bw() + theme(legend.position = "right", legend.key = element_blank(), legend.text = element_text(colour = "black", size = 12), legend.title = element_blank(), axis.text.x = element_text(size = 12, angle = 45, vjust = +0.5), axis.text.y = element_text(size = 12), axis.title = element_text(size = 14), panel.grid.major = element_blank(), panel.grid.minor = element_blank(), plot.margin = unit(c(0, 0, 0, 0), "line")) #Top plot (line) p2 <- ggplot(testD_agg, aes(x = x, y = z)) + geom_line() + xlab(NULL) + coord_cartesian(xlim = c(0, 100), ylim = c(0, max(testD_agg$z))) + theme_bw() + theme(legend.position = "none", legend.key = element_blank(), legend.text = element_text(colour = "black", size = 12), legend.title = element_text(size = 12, face = "plain"), axis.text.x = element_blank(), axis.text.y = element_text(size = 12), axis.title = element_text(size = 14), axis.ticks.x = element_blank(), panel.grid.major = element_blank(), panel.grid.minor = element_blank(), plot.margin = unit(c(0.5, 0.5, 0, 0), "line")) #Create gtables gp <- ggplotGrob(p) gp2 <- ggplotGrob(p2) #Add space to the right of the top plot with width equal to the legend of the bottomplot legend.width <- gp$widths[7:8] #obtain the width of the legend in pff2 gp2 <- gtable_add_cols(gp2, legend.width, 4) #add a colum to pff with with legend.with #combine the plots cg <- rbind(gp2, gp, size = "last") #set the ratio of the plots panels <- cg$layout$t[grep("panel", cg$layout$name)] cg$heights[panels] <- unit(c(2,3), "null") #remove white spacing between plots cg <- gtable_add_rows(cg, unit(0, "npc"), pos = nrow(gp)) pdf("test.pdf", width = 8, height = 7) print(grid.draw(cg)) dev.off() #The following did not help solve my problem but I think I got close old.height <- cg$grobs[[16]]$heights[2] #It seems the height of the legend is given in "mm", change to "npc"? gp$grobs[[8]]$grobs[[1]]$heights <- c(rep(unit(0, "npc"), 3), rep(unit(1/4, "npc"), 4), rep(unit(0, "mm"),1)) #this does allow for adjustment of the heights but not the exact control I need. 

My evidence has a few more categories, but the essence is the same. Here is the image created using the code above and annotated with what I would like to do.

Thanks in advance! Maarten

Answer 1

There seem to be two sets of heights that need to be adjusted: the legend key heights and the overall legend height. Choosing cg from my verb, I extract the legend, make height adjustments, and then insert the legendary grob back into the layout.

 leg = gtable_filter(cg, "guide-box") library(grid) # Legend keys leg[[1]][[1]][[1]][[1]]$heights = unit.c(rep(unit(0, "mm"), 3), rep(unit(1/4, "npc"), 4), unit(0, "mm")) # Legend leg[[1]][[1]]$heights[[3]] = sum(rep(unit(0, "mm"), 3), rep(unit(1/4, "npc"), 4), unit(0, "mm")) # grid.draw(leg) # Check that heights are correct cg.new = gtable_add_grob(cg, leg, t = 17, l = 8) grid.newpage() grid.draw(cg.new)