Question

I plotted a facet plot using ggplot and here is the plot

The problem I have is, The facets(labels) are sorted alphabetically (Ex: E1, E10, E11,E13, E2, E3, I1, I10, I2) but I need them to be a custom order like E1, I1, E2, I2, E3, E10, I10, E11, E13.

How can I do that ?

Answer 1

Don’t rely on the default ordering of levels imposed by factor() or internally by ggplot if the grouping variable you supply is not a factor. Set the levels explicitly yourself.

dat <- data.frame(x = runif(100), y = runif(100), 
                  Group = gl(5, 20, labels = LETTERS[1:5]))
head(dat)
with(dat, levels(Group))

What if I want them in this arbitrary order?

set.seed(1)
with(dat, sample(levels(Group)))

To do this, set the levels the way you want them.

set.seed(1) # reset the seed so I get the random order form above
dat <- within(dat, Group <- factor(Group, levels = sample(levels(Group))))
with(dat, levels(Group))

Now we can use this to have the panels drawn in the order we want:

require(ggplot2)
p <- ggplot(dat, aes(x = x)) + geom_bar()
p + facet_wrap( ~ Group)

Which produces: