Avoid overlapping x-axis labels in ggplot facet grid

Question

I am trying to plot a facet grid of growth plots and my labels at the ends of each plot are overlapping with the each other. Here is sample code using the mpg data:

print(ggplot(data = aggregate(hwy~class+year, data=mpg, mean), aes(x = year, y=hwy))+
    geom_line(aes(group = 1))+
    geom_point()+
    facet_wrap(~class,  nrow = 2)+
    xlab("Year")+
    scale_x_discrete(limits=unique(mpg$year)))

How do I prevent this overlapping, perhaps by moving the tick marks and labels in from the edge of the plot. I tried using the margin within theme, but I did not have success with this either. Thank you for your help.

Cosenza

The easiest soln. is too increase the width of your graphics window or output device. Howvever, you could rotate the labels p + theme(axis.text.x = element_text(angle=-90, vjust=0.5)). Or you could add a little space using expand..scale_x_discrete(expand=c(0.5, 0.5), limits=unique(mpg$year)) – Illuminating

Answer 1

I presume what you are after is adjusting the horizontal spacing between facet panels with panel.spacing.x in theme (tested with ggplot2_3.0.0).

ggplot(data = aggregate(hwy~class+year, data=mpg, mean), aes(x = year, y=hwy))+
  geom_line(aes(group = 1))+
  geom_point()+
  facet_wrap(~class,  nrow = 2)+
  xlab("Year")+
  scale_x_discrete(limits=unique(mpg$year)) +
  theme(panel.spacing.x = unit(4, "mm"))

Before

After - using panel.spacing.x()

Brucebrucellosis

Answer 2

The answer by @Valentin_Ștefan is fantastic is probably sufficient for most circumstances. However, when there are space limitations, it is probably best just to change the axis text alignment.

ggplot(data = aggregate(hwy~class+year, data=mpg, mean), aes(x = year, y=hwy))+
        geom_line(aes(group = 1))+
        geom_point()+
        facet_wrap(~class,  nrow = 2)+
        xlab("Year")+
        scale_x_discrete(limits=unique(mpg$year))+ 
        theme(axis.text.x=element_text(hjust=c(0,1)))

This solution does have an issue in that element_text() does not officially accept vectorized inputs and so creates this warning message.

2: Vectorized input to `element_text()` is not officially supported.
ℹ Results may be unexpected or may change in future versions of ggplot2. 

If anyone knows an official way to do this, feel free to update or comment.

Greatgranduncle