A generic auxiliary function that produces a numeric vector which
will sort in the same order as x.
xtfrm(x)an R object.
A numeric (usually integer) vector of the same length as x.
This is a special case of ranking, but as a less general function than
rank is more suitable to be made generic. The default
method is similar to rank(x, ties.method = "min",
na.last = "keep"), so NA values are given rank NA and all
tied values are given equal integer rank.
The factor method extracts the codes.
The default method will unclass the object if
is.numeric(x) is true but otherwise make use of
== and > methods for the class of x[i] (for
integers i), and the is.na method for the class of
x, but might be rather slow when doing so.
This is an internal generic primitive, so S3 or S4 methods can be written for it.