Annotate values above bars (ggplot faceted)

Question

One of my favorite tricks in base graphics is a pickup from Bill Dunlap. Being able to place numeric values (or any values) above bars in a bar plot (I don't use it but once in a while but love it).

mtcars2 <- mtcars[order(-mtcars$mpg), ] par(cex.lab=1, cex.axis=.6,      mar=c(6.5, 3, 2, 2) + 0.1, xpd=NA) #shrink axis text and increas bot. mar.  barX <- barplot(mtcars2$mpg,xlab="Cars", main="MPG of Cars",     ylab="", names=rownames(mtcars2), mgp=c(5,1,0),    ylim=c(0, 35), las=2, col=mtcars2$cyl)  mtext(side=2, text="MPG", cex=1, padj=-2.5) text(cex=.5, x=barX, y=mtcars2$mpg+par("cxy")[2]/2, mtcars2$hp, xpd=TRUE)  

Which gives you:

I want to be able to do the same sort of annotation with faceted bar plots in ggplot. Obviously the values would also have to be by the same two variables you faceted to plot by so you could obtain them with ftable. I'd like to take the ftable results below (for non zero values) and place them above their respective bars.

library(ggplot2) mtcars2 <- data.frame(id=1:nrow(mtcars), mtcars[, c(2, 8:11)]) mtcars2[, -1] <- lapply(mtcars2[, -1], as.factor)  with(mtcars2, ftable(cyl, gear, am))  ggplot(mtcars2, aes(x=cyl)) + geom_bar() +      facet_grid(gear~am) 

This seems pretty difficult to me but maybe it'll be easier than I think. Thank you in advance for thinking about this problem.

Answer 1

Am I right in thinking that you just want the count (i.e the height) of each non-zero bar? If so, you can achieve that with

ggplot(mtcars2, aes(x=cyl)) +    geom_bar() +    facet_grid(gear~am) +    stat_bin(geom="text", aes(label=..count.., vjust=-1)) 

Which produces this graph (you may have to do some tweaking to get that highest label to show):

count is a new variable in a dataframe created by stat_bin(), which is why you have to reference it with ..count..