How can I make a legend in ggplot2 the same height as my plot?

Question

I created a simple graph in R (version R version 3.0.1 (2013-05-16)) using ggplot2 (version 0.9.3.1), which shows the correlation coefficients for a dataset. Currently, the legend color bar on the right side of the graph is part of the entire graph size.

I would like the legend color bar to be the same height as the graph. I thought I could use legend.key.height for this, but I found that it is not. I examined the grid package unit function and found that there were some normalized units, but when I tried them ( unit(1, "npc") ), the color bar was too high and left the page.

How to make a legend the same height as the plot itself?

The following is a complete example:

 # Load the needed libraries library(ggplot2) library(grid) library(scales) library(reshape2) # Generate a collection of sample data variables = c("Var1", "Var2", "Var3") data = matrix(runif(9, -1, 1), 3, 3) diag(data) = 1 colnames(data) = variables rownames(data) = variables # Generate the plot corrs = data ggplot(melt(corrs), aes(x = Var1, y = Var2, fill = value)) + geom_tile() + geom_text(parse = TRUE, aes(label = sprintf("%.2f", value)), size = 3, color = "white") + theme_bw() + theme(panel.border = element_blank(), axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1), aspect.ratio = 1, legend.position = "right", legend.key.height = unit(1, "inch")) + labs(x = "", y = "", fill = "", title = "Correlation Coefficients") + scale_fill_gradient2(limits = c(-1, 1), expand = c(0, 0), low = muted("red"), mid = "black", high = muted("blue")) 

Answer 1

Seems pretty complicated, the closest I got it,

 ## panel height is 1null, so we work it out by subtracting the other heights from 1npc ## and 1line for the default plot margins panel_height = unit(1,"npc") - sum(ggplotGrob(plot)[["heights"]][-3]) - unit(1,"line") plot + guides(fill= guide_colorbar(barheight=panel_height)) 

Unfortunately, the vertical rationale is a bit off.

Answer 2

It's dirty, but based on this answer , and by delving into ggplot grob, the legend can be placed for sure.

 # Load the needed libraries library(ggplot2) library(gtable) # library(grid) library(scales) library(reshape2) # Generate a collection of sample data variables = c("Var1", "Var2", "Var3") data = matrix(runif(9, -1, 1), 3, 3) diag(data) = 1 colnames(data) = variables rownames(data) = variables # Generate the plot corrs = data plot = ggplot(melt(corrs), aes(x = Var1, y = Var2, fill = value)) + geom_tile() + theme_bw() + theme(panel.border = element_blank()) + theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1)) + theme(aspect.ratio = 1) + # theme(legend.position = "right", legend.key.height = unit(1, "inch")) + labs(x = "", y = "", fill = "", title = "Correlation Coefficients") + scale_fill_gradient2(limits = c(-1, 1), breaks = c(-1, -.5, 0, .5, 1), expand = c(0,0), low = muted("red"), mid = "black", high = muted("blue")) + # Modified line geom_text(parse = TRUE, aes(label = sprintf("%.2f", value)), size = 3, color = "white") + scale_x_discrete(expand = c(0,0)) + # New line scale_y_discrete(expand = c(0,0)) # New line plot # Get the ggplot grob gt = ggplotGrob(plot) # Get the legend leg = gtable_filter(gt, "guide-box") # Raster height leg[[1]][[1]][[1]][[1]][[1]][[2]]$height = unit(1, "npc") # Positions for labels and tick marks - five breaks, therefore, five positions pos = unit.c(unit(0.01,"npc"), unit(.25, "npc"), unit(.5, "npc"), unit(.75, "npc"), unit(.99, "npc")) # Positions the labels leg[[1]][[1]][[1]][[1]][[1]][[3]]$y = pos # Positions the tick marks leg[[1]][[1]][[1]][[1]][[1]][[5]]$y0 = pos leg[[1]][[1]][[1]][[1]][[1]][[5]]$y1 = pos # Legend key height ? leg[[1]][[1]][[1]][[1]]$heights = unit.c(rep(unit(0, "mm"), 3), unit(1, "npc"), unit(0, "mm")) # Legend height leg[[1]][[1]]$heights[[3]] = sum(rep(unit(0, "mm"), 3), unit(1, "npc"), unit(0, "mm")) # grid.draw(leg) # Check on heights and y values # gtable_show_layout(gt) # Manually locate position of legend in layout gt.new = gtable_add_grob(gt, leg, t = 6, l = 8) # Draw it grid.newpage() grid.draw(gt.new)