How to change order of boxplots when using ggplot2?

Question

This question follows from this other one. I was unable to implement answers there.

Define:

df2 <- data.frame(variable=rep(c("vnu.shr","vph.shr"),each=10),
        value=seq(1:20))

Plot:

require(ggplot2)
qplot(variable,value, data=df2,geom="boxplot")+
geom_jitter(position=position_jitter(w=0.1,h=0.1))

I would like to have the boxplots in the reverse order (e.g. one in right on left and so on).

I have tried various ways of reordering the factors using levels, ordered, relevel, rev and so on, but I simply cannot seem to get the syntax right.

Answer 1

Have you tried this:

df2$variable <- factor(df2$variable,
    levels = c('vph.shr','vnu.shr'),ordered = TRUE)

I just picked an ordering there, since my system is configured slightly differently than yours I suspect, so my 'default ordering' may differ. But you can just switch the position of levels when specifying them.

A few other options, depend on your tastes:

For just reversing the current ordering:

factor(df2$variable,levels = rev(levels(df2$variable)),ordered = TRUE)

or you can use subsetting to specify a specific ordering if you don't want to type out each level by hand:

factor(df2$variable,levels = levels(df2$variable)[1:2],ordered = TRUE)

Answer 2

You've already accepted a (perfectly fine) solution, but here's another option using relevel(). I'm not sure why it wasn't working for you?

#default plot
ggplot(df2, aes(variable, value)) + geom_boxplot()

#Reverse reverse!
df2$variable2 <- with(df2, relevel(variable, "vph.shr"))
ggplot(df2, aes(variable2, value)) + geom_boxplot()