New levels. The length of
value must equal the current number of levels
for
x.
If the new levels in
value are not unique, the old levels will be merged into the
unique new levels.
Note that in this case the numeric codes; i.e.,
codes(x), will change
as will the length of the levels attribute.
This is a method for the function levels<-() for objects inheriting from class
factor.
SEE ALSO:
(which is called when non-unique levels are assigned)