changing axis size in ggplot - r

Question

I'm working on a plot where I would like to change the axis thickness to match the boarder of the facet labels. Somehow axis.line = element_line(color="black", size=0.5) doesn't work - any ideas why?
This is my code...
ggplot(datgg_final, aes(y = total_GLS, x = timing)) +
geom_boxplot(aes(fill = genotype)) +
facet_grid(col=vars(genotype)) +
theme(legend.position = "none") +
scale_fill_manual(values=c("#0496FF", "#53A548")) +
ggtitle("Effect of Timing") +
xlab("Days since Defence Induction") +
ylab("Total Glucosinolates (µmol g^-1 DW)") +
theme(strip.background = element_rect(color = "black", fill ="white", size=0.5, linetype="solid"),
axis.line = element_line(color="black", size=0.5))
... and the plot:
enter image description here
Even in most basic plots I cannot change any axis settings (except the linetype), this code just shows the normal boxplot, no red axes, no change in line size:
ggplot(datgg_final, aes(y=total_GLS, x=timing)) +
geom_boxplot() +
theme(axis.line=element_line(size=0.5, color="red"))

Answer 1

Fortunately, this seems to be a simple clipping issue. Unfortunately, this can't be adressed with the normal ggplot interface (as far as I know), but you could mess around in the gtable to produce the plot you want.
Consider the following plot:
library(ggplot2)
library(grid)
g <- ggplot(iris, aes(Sepal.Width, Sepal.Length)) +
geom_point() +
facet_grid(~ Species) +
theme(strip.background.x = element_rect(colour = "black", fill = "white",
size = 0.5, linetype = "solid"),
axis.line = element_line(colour = "black", size = 0.5))
g
You can see that the apparent linewidths of the facet strips and the axes are unequal. We can turn of the clipping by messing around in the gtable:
# Convert plot to gtable
gt <- ggplotGrob(g)
# Find the strips
is_strip <- grep("strip", gt$layout$name)
# Turn off clipping at highest level
gt$layout$clip[is_strip] <- "off"
# Turn off clipping at the strip level
gt$grobs[is_strip] <- lapply(gt$grobs[is_strip], function(strip) {
strip$layout$clip <- "off"
strip
})
# Plot
grid.newpage(); grid.draw(gt)
Now the apparent linewidths are the intended linewidths, but it took quite some extra steps to get there. If somebody has a more elegant solution, be welcome to post an alternative.