GGPLOT Facet: How to Add Space Between Labels on the Top of the Chart and the Plot Border

Create a faceted box plot with p-values labels

library(ggpubr)
p <- ggboxplot(
   ToothGrowth, x = "supp", y = "len",
   color = "supp", palette = "jco", 
   facet.by = "dose", short.panel.labs = FALSE
   ) +
   stat_compare_means(
      method = "t.test", label = "p.format",
      comparisons=list(c("OJ","VC"))
      )
p

Solution 1: Expanding the y-axis using the ggplot2 function expansion()

Key R function:

expansion(mult = 0, add = 0)

• mult: vector of multiplicative range expansion factors. If length 1, both the lower and upper limits of the scale are expanded outwards by the mult factor. If length 2, the lower limit is expanded by mult[1] and the upper limit by mult[2] factors.
• add: vector of additive range expansion constants. If length 1, both the lower and upper limits of the scale are expanded outwards by add units. If length 2, the lower limit is expanded by add[1] and the upper limit by add[2] constants.

# No space below the box plots
# Add 10% space on the y-axis above the box plots
p +
   scale_y_continuous(expand = expansion(mult = c(0, 0.1)))

Solution 2: Using the ggplot2 function ylim()

This is only useful if the scales are similar for the different facet panels.

p + ylim (c(0, 45))

Conclusion

This article describes how to add space between labels and the ggplot top border when using the facet functions. This can be easily achieved using the combinations of scale_y_continuous() and expansion(). Note that it’s also possible to combine scale_x_continuous() and expansion() for adding spaces between data and the x-axis.