Original figure

library(ggplot2)
ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + 
  geom_boxplot()

“Zoom in” with scales

Data points outside the limits are considered to be NA. Note that this will alter all calculated geoms.

ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + 
  geom_boxplot() + 
  scale_y_continuous(limits = c(20, 25))
## Warning: Removed 24 rows containing non-finite values (stat_boxplot).

“Zoom in” with coord

This doesn’t affect the values

ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + 
  geom_boxplot() + 
  coord_cartesian(ylim = c(20, 25))

Note that you can use only one coord. Only the last one will have an effect on the plot.

ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + 
  geom_boxplot() + 
  coord_cartesian(ylim = c(20, 25)) + 
  coord_flip()

ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + 
  geom_boxplot() + 
  coord_flip() + 
  coord_cartesian(ylim = c(20, 25))

Set the limits in coord_flip to get the effects of both.

ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + 
  geom_boxplot() + 
  coord_flip(ylim = c(20, 25))