reorder.factor
Reorder the Levels of a Factor
Reorder the levels of a factor
 Keywords
 manip
Usage
"reorder"(x, X, FUN, ..., order = is.ordered(x), new.order, sort = SortMixed)
Arguments
 x
 factor
 X
 auxillary data vector
 FUN
 function to be applied to subsets of
X
determined byx
, to determine factor order  ...
 optional parameters to
FUN
 order
 logical value indicating whether the returned
object should be an
ordered
factor  new.order
 a vector of indexes or a vector of label names giving the order of the new factor levels
 sort
 function to use to sort the factor level names, used only
when
new.order
is missing
Details
This function changes the order of the levels of a factor. It can do
so via three different mechanisms, depending on whether, X
and FUN
, new.order
or sort
are provided.
If X
and Fun
are provided: The data in X
is grouped by the levels of x
and FUN
is applied.
The groups are then sorted by this value, and the resulting order is
used for the new factor level names.
If new.order
is provided: For a numeric vector, the new factor
level names are constructed by reordering the factor levels according
to the numeric values. For vectors, new.order
gives the list of
new factor level names. In either case levels omitted from
new.order
will become missing (NA
) values.
If sort
is provided (as it is by default): The new
factor level names are generated by applying the supplied function
to the existing factor level names. With sort=mixedsort
the
factor levels are sorted so that combined numeric and character
strings are sorted in according to character rules on the character
sections (including ignoring case), and the numeric rules for the
numeric sections. See mixedsort
for details.
Value

A new factor with reordered levels
See Also
Examples
# Create a 4 level example factor
trt < factor( sample( c("PLACEBO", "300 MG", "600 MG", "1200 MG"),
100, replace=TRUE ) )
summary(trt)
# Note that the levels are not in a meaningful order.
# Change the order to something useful
# default "mixedsort" ordering
trt2 < reorder(trt)
summary(trt2)
# using indexes:
trt3 < reorder(trt, new.order=c(4, 2, 3, 1))
summary(trt3)
# using label names:
trt4 < reorder(trt, new.order=c("PLACEBO", "300 MG", "600 MG", "1200 MG"))
summary(trt4)
# using frequency
trt5 < reorder(trt, X=as.numeric(trt), FUN=length)
summary(trt5)
# drop out the '300 MG' level
trt6 < reorder(trt, new.order=c("PLACEBO", "600 MG", "1200 MG"))
summary(trt6)