position_dodge and nudge_y together - r

Question

I am trying to add labels (letters) above a barplot using ggplot2 function geom_text. My bars are separated using position=position_dodge() and so I need to apply the same for the new labels. However I would like to use also nudge_y to separate the labels from the bar. If I try to use both together R complains that I can use only one of either options. I'd like to do something like this:
Tukey.labels <- geom_text(data=stats,
aes(x=factor(Treatment2), y=x.mean,
label=Tukey.dif),
size=4, nudge_y=3, # move letters in Y
position=position_dodge(0.5)) # move letters in X
To create something like this image Does anybody knows a possibility to shift all my labels the same distance in Y while doing position_dodge at the same time? I could not find answer for this in other posts

Answer 1

Hard to troubleshoot without a reproducible example. Hopefully this helps:
library(dplyr); library(ggplot2)
ggplot(mtcars %>% rownames_to_column("car") ,
aes(as.factor(cyl), mpg, group = car)) +
geom_col(position = position_dodge(0.9)) +
geom_errorbar(aes(ymin = mpg - wt,
ymax = mpg + wt),
position = position_dodge(0.9)) +
geom_text(aes(label = gear, y = mpg + wt), vjust = -0.5,
position = position_dodge(0.9))

Answer 2

In the spirit of the original question, one can easily combine ggplot's position_nudge and position_dodge like this:
position_nudgedodge <- function(x = 0, y = 0, width = 0.75) {
ggproto(NULL, PositionNudgedodge,
x = x,
y = y,
width = width
)
}
PositionNudgedodge <- ggproto("PositionNudgedodge", PositionDodge,
x = 0,
y = 0,
width = 0.3,
setup_params = function(self, data) {
l <- ggproto_parent(PositionDodge,self)$setup_params(data)
append(l, list(x = self$x, y = self$y))
},
compute_layer = function(self, data, params, layout) {
d <- ggproto_parent(PositionNudge,self)$compute_layer(data,params,layout)
d <- ggproto_parent(PositionDodge,self)$compute_layer(d,params,layout)
d
}
)
Then you can use it like this:
Tukey.labels <- geom_text(data=stats,
aes(x=factor(Treatment2), y=x.mean, label=Tukey.dif),
size=4,
position=position_nudgedodge(y=3,width=0.5)
)