How to modify whiskers of a boxplot in ggplot2?

Question

I'll start with an MWE:

library(ggplot2)



p <- ggplot(mtcars, aes(factor(cyl), mpg, fill = factor(am)))

p + geom_boxplot()

I'd like to modify the colour of the whiskers, e.g., set it to red. I don't think it's possible to do this directly both

geom_boxplot

, so this is my workaround:

library(Hmisc)



stat_sum_df <- function(fun, geom = "crossbar", ...) {

  stat_summary(fun.data = fun, geom = geom, width = 0.4, ...)

}



p + stat_boxplot(geom = 'linerange', colour = "red", position = "dodge) +

    stat_sum_df("median_hilow", conf.int = 0.5, position = "dodge")

The line ranges are stacked on top of each other. So next try:

p + stat_boxplot(geom = 'linerange', colour = "red", position = position_dodge(width = .5)) +

   stat_sum_df("median_hilow",conf.int=0.5, position = position_dodge(width = .5))

Looks nicer, but now there is a fixed space between the boxes (compare cyl = 8 on first and third plot). As I'm going to use this code for different number of levels of

am

(of course in my real data, it's not

am

), I don't know in advance how wide the boxes themselves will be, so I can't set a fixed

width

for the

linerange

without specifying a fixed

width

for the boxes.

Is there a way either to selectively modify whiskers of a

boxplot

or to adjust space between

linerange

elements according to space between the boxes?

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Answer 1

How about plotting two boxplots on top of each other. One with red lines and a second one on top without any wiskers at all.

p + geom_boxplot(color="red") + geom_boxplot(aes(ymin=..lower.., ymax=..upper..))

How to modify whiskers of a boxplot in ggplot2?

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