R – How to get a reversed, log10 scale in ggplot2

ggplot2r

I'd like to make a plot with a reversed, log10 x scale using ggplot2:

require(ggplot2)
df <- data.frame(x=1:10, y=runif(10))
p <- ggplot(data=df, aes(x=x, y=y)) + geom_point()

However, it seems that I can either a log10 scale or a reversed scale:

p + scale_x_reverse() + scale_x_log10()

log10 scale, but not reversed

p + scale_x_reverse()

reversed scale, but not log10

I guess this is logical, if a layer can only have one scale. And certainly I could hack it by doing the log transform on the dataframe myself, df$xLog <- log10(df$x)
but that solution is a seems contrary to the spirit of ggplot. Is there a way to get this kind of plot without doing data transformations external to the ggplot call?

Best Answer

The link that @joran gave in his comment gives the right idea (build your own transform), but is outdated with regard to the new scales package that ggplot2 uses now. Looking at log_trans and reverse_trans in the scales package for guidance and inspiration, a reverselog_trans function can be made:

library("scales")
reverselog_trans <- function(base = exp(1)) {
    trans <- function(x) -log(x, base)
    inv <- function(x) base^(-x)
    trans_new(paste0("reverselog-", format(base)), trans, inv, 
              log_breaks(base = base), 
              domain = c(1e-100, Inf))
}

This can be used simply as:

p + scale_x_continuous(trans=reverselog_trans(10))

which gives the plot:

enter image description here

Using a slightly different data set to show that the axis is definitely reversed:

DF <- data.frame(x=1:10,  y=1:10)
ggplot(DF, aes(x=x,y=y)) + 
  geom_point() +
  scale_x_continuous(trans=reverselog_trans(10))

enter image description here

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