How to make gap between x and y axis and protruded ticks in ggplot2

Question

How can I create the following style of graph:

Notice the gap between x-y axis (red circle) and protruded ticks in x-y axis (arrow).

At best I can do is this now:

library(ggplot2)
p <- ggplot(mpg, aes(class, hwy)) +
     geom_boxplot() +
     theme_bw(base_size=10) 

p

Answer 1

EDIT: From ggplot2 3.5.0 onwards you can do guide_axis(cap = "both"). I recommend this over ggh4x::guide_axis_truncated().

Originally posted as an answer to a related question, I was encouraged to share my answer here as well.

The ggh4x package has a truncated axis guide that solves this problem by taking advantage of position guide customisation introduced in ggplot2 v3.3.0. Because it uses the guide system directly instead of working through a geom, it is responsive to theme settings just as regular axes. (Disclaimer: I'm the author of ggh4x).

By default, it truncates the axis to the outermost breaks, but this can be adjusted.

library(ggplot2)
library(ggh4x)

ggplot(mpg, aes(class, hwy)) +
  geom_boxplot() +
  guides(x = "axis_truncated", y = "axis_truncated") +
  theme(axis.line = element_line(colour = "black"))

^{Created on 2021-04-19 by the reprex package (v1.0.0)}

Answer 2

The bars on the top and bottom of the lines are added with

geom_errorbar(aes(ymin = lower, ymax = upper), width = 0.2)

or by adding geom to another layer.

stat_summary(fun.data = mean_sdl,
             fun.args = list(mult = 1),
             geom = "errorbar",
             width = 0.1)

Answer 3

You can achieve something similar using ggthemes which provides geom_rangeframe and theme_tufte.

library(ggplot2)
library(ggthemes)
ggplot(mpg, aes(class, hwy)) + 
  geom_boxplot() + 
  geom_rangeframe() + 
  theme_tufte() +
  theme(axis.ticks.length = unit(7, "pt"))

More inspiration here.

Answer 4

One option is to remove the built-in axis lines and then use geom_segment to add axes with a gap. In order to make it easier to get the broken axis lines in the right place, we also use scale_y_continuous to specify exactly where we want the axis breaks and limits. The code also shows how to increase the size of the tick marks.

ggplot(data=mpg, aes(class, hwy)) +
  geom_segment(y=10, yend=50, x=0.4, xend=0.4, lwd=0.5, colour="grey30", lineend="square") +
  geom_segment(y=5, yend=5, x=1, xend=length(unique(mpg$class)), 
               lwd=0.5, colour="grey30", lineend="square") +
  geom_boxplot() +
  scale_y_continuous(breaks=seq(10,50,10), limits=c(5,50), expand=c(0,0)) +
  theme_classic(base_size=12) +
  theme(axis.line = element_blank(),
        axis.ticks.length = unit(7,"pt"))