Question

Here is a boxplot:

qplot(cyl, mpg, data=mtcars) +
  geom_boxplot() +
  scale_y_continuous()

that looks like this:

Now I add limits to the y axis:

qplot(cyl, mpg, data=mtcars) +
  geom_boxplot() +
  scale_y_continuous(limits=c(0,20))

and the whole picture changes:

How do I get the same picture as the first, just with a ‘viewport’ showing y=0 to 20?

And .. what is the second picture? It looks like there is actually data missing (example: 3-4 points for cyl=4).

Answer 1

From joran’s comment, this works:

qplot(cyl, mpg, data=mtcars) +
  geom_boxplot() +
  coord_cartesian(ylim=c(0,20))

From the docs:

There are two ways of zooming the plot display: with scales or with
coordinate systems. They work in two rather different ways.

Setting the limits on a scale will throw away all data that’s not
inside these limits. This is equivalent to plotting a subset of the
original data

Setting the limits on the coordinate system performs a visual zoom
the data is unchanged, and we just view a small portion of the
original plot.

Thanks joran!