Apply two transformations on one axis

Question

I have found coord_trans, but I\'d like to apply log10 and reverse to my x-axis. I tried applying two transformation

ggplo         


        

Answer 1

A quick and easy way is to apply one of the transformations directly to the data and use the other with the plot function.

e.g.

ggplot(iris, aes(log10(Sepal.Length), log10(Sepal.Width), colour = Species)) + 
geom_point() + coord_trans(x="reverse", y="reverse")

Note: the reverse transformation does not work with the iris data but you get the idea.

Answer 2

I wandered in here looking for a 'composition of scales' function. I think one might be able to write such a thing as follows:

# compose transforms a and b, applying b first, then a:
`%::%`  <- function(atrans,btrans) {
  mytran <- scales::trans_new(name      = paste(btrans$name,'then',atrans$name),
                              transform = function(x) { atrans$transform(btrans$transform(x)) },
                              inverse   = function(y) { btrans$inverse(atrans$inverse(y)) },
                              domain    = btrans$domain,  # this could use improvement...
                              breaks    = btrans$breaks,  # not clear how this should work, tbh
                              format    = btrans$format)

}

ph <- ggplot(mtcars, aes(wt, mpg)) +
  geom_point() +
  scale_y_continuous(trans=scales::reverse_trans() %::% scales::log10_trans())
print(ph)

Answer 3

You can define new transformations using trans_new.

library(scales)
log10_rev_trans <- trans_new(
  "log10_rev",
  function(x) log10(rev(x)),
  function(x) rev(10 ^ (x)),
  log_breaks(10),
  domain = c(1e-100, Inf)
)

p <- ggplot(mtcars, aes(wt, mpg)) +
   geom_point()   

p + coord_trans(y = log10_rev_trans)