theme: axis.line elements do not behave as documented

[mschubert]

I'm using ggplot2_4.0.1 and want to change the axis line theme. According to the documentation, I can use the axis.line.* elements.

However, this does not quite work as expected:

# this works: line is drawn as expected
ggplot(mtcars) +
  geom_point(aes(x = hp, y = mpg)) +
  theme(axis.line.y.left = element_line()) # same for axis.line.x.bottom

# this doesn't work: no line is shown on the right side
ggplot(mtcars) +
  geom_point(aes(x = hp, y = mpg)) +
  theme(axis.line.y.right = element_line()) # same for axis.line.x.top

# this doesn't work: lines on the top/right are documented to be interited, but aren't
ggplot(mtcars) +
  geom_point(aes(x = hp, y = mpg)) +
  theme(axis.line = element_line()) # same for axis.line.x, axis.line.y

[teunbrand]

Thanks for the report! The theme elements work if you place axes on these positions, which are absent by default.
You can use scale_y_continuous(position = 'right'), scale_x_continuous(position = "top") or use the secondary axes like guides(x.sec = "axis", y.sec = "axis") to have these appear.

[mschubert]

Yes, thanks! I realized this after I posted as well.

If you want both, it's also possible to add a secondary axis:

ggplot(mtcars) +
  geom_point(aes(x = hp, y = mpg)) +
  scale_x_continuous(sec.axis = sec_axis(transform=identity)) +
  scale_y_continuous(sec.axis = sec_axis(transform=identity)) +
  theme(axis.line.y.right = element_line())