You will need to define a method for this method if you want to extend
ggplot2 to handle new types of data. If you simply want to pass the vector
through as an additional aesthetic, return
A character vector of scale types. These will be tried in turn
to find a default scale. For example, if
c("foo", "bar") and the vector is used with the colour aesthetic,
ggplot2 will first look for
scale_type(1:5)#>  "continuous"scale_type("test")#>  "discrete"scale_type(Sys.Date())#>  "date" "continuous"