[R] ggplot: dodge positions

[Thaler,Thorn,LAUSANNE,Applied Mathematics]

Dear all,

I want to get a series of boxplots (grouped by two factors) and I want to overlay the original observations and the following code does almost what I want:

library(ggplot)
ddf <- data.frame(x=factor(rep(LETTERS[1:4], each=30)), y = runif(120,0,10), grp = factor(rep(rep(1:3, 10), 4)))
ggplot(ddf, aes(x, y, colour=grp)) + geom_boxplot() + geom_point()

Yet the position of the points and the position of the boxes on the x-axis is not the same. I would like that the points are shifted accordingly, such that they line up with the boxplots. I tried position_dodge:

ggplot(ddf, aes(x, y, colour=grp)) + geom_boxplot() + geom_point(aes(ymax=max(y)), position = position_dodge(width=.75))

but that did not really help, as all points are now dodged and I just want to have a fixed offset for each subgroup of points such that the boxplot and the points are aligned. Any ideas?


Kind Regards,

Thorn Thaler
Mathematician

Applied Mathematics 
Nestec Ltd,
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