Reorder an x or y axis within facets

Reorder a column before plotting with faceting, such that the values are ordered within each facet. This requires two functions: reorder_within applied to the column, then either scale_x_reordered or scale_y_reordered added to the plot. This is implemented as a bit of a hack: it appends ___ and then the facet at the end of each string.

reorder_within(x, by, within, fun = mean, sep = "___", ...)

scale_x_reordered(..., sep = "___")

scale_y_reordered(..., sep = "___")

Arguments

x	Vector to reorder.
by	Vector of the same length, to use for reordering.
within	Vector of the same length that will later be used for faceting
fun	Function to perform within each subset to determine the resulting ordering. By default, mean.
sep	Separator to distinguish the two. You may want to set this manually if ___ can exist within one of your labels.
...	In reorder_within arguments passed on to reorder. In the scale functions, extra arguments passed on to scale_x_discrete or scale_y_discrete.

Source

"Ordering categories within ggplot2 Facets" by Tyler Rinker: https://trinkerrstuff.wordpress.com/2016/12/23/ordering-categories-within-ggplot2-facets/

Examples

if (FALSE) {
library(tidyr)
library(ggplot2)

iris_gathered <- gather(iris, metric, value, -Species)

# reordering doesn't work within each facet (see Sepal.Width):
ggplot(iris_gathered, aes(reorder(Species, value), value)) +
  geom_boxplot() +
  facet_wrap(~ metric)

# reorder_within and scale_x_reordered work.
# (Note that you need to set scales = "free_x" in the facet)
ggplot(iris_gathered, aes(reorder_within(Species, value, metric), value)) +
  geom_boxplot() +
  scale_x_reordered() +
  facet_wrap(~ metric, scales = "free_x")
}