r - How to expand axis asymmetrically with ggplot2 without setting limits manually? -

i want bottom axis barplot zero, top expanded small amount (according scale). however, plotting output of stat_summary not have maximum value available me, , using facets scale="free_y" cannot manually set them. otherwise use baptiste's trick of adding geom_blank. know read off values , create data frame upper bounds manually, can set without having hard-code limits?

the other option compute means outside of function call , plot without calling stat_summary (this way have upper bounds directly each facet), there way around this?

example:

ggplot(mtcars)+   stat_summary(aes(cyl,mpg),                fun.y="mean",                geom="bar")+   scale_y_continuous(expand=c(0,0))+   facet_grid(carb~.,"free_y") 

you can "extend" ggplot creating scale custom class , implementing internal s3 method scale_dimension so:

library("scales") scale_dimension.custom_expand <- function(scale, expand = ggplot2:::scale_expand(scale)) {   expand_range(ggplot2:::scale_limits(scale), expand[[1]], expand[[2]]) }  scale_y_continuous <- function(...) {   s <- ggplot2::scale_y_continuous(...)   class(s) <- c('custom_expand', class(s))   s } 

this example of overriding default scale. now, desired result specify expand so

qplot(1:10, 1:10) + scale_y_continuous(expand=list(c(0,0.1), c(0,0))) 

where first vector in list multiplicative factor, second additive part , first (second) element of each vector corresponds lower (upper) boundary.