ReorderFactor.RdReorder the levels of a factor
# S3 method for class 'factor'
reorder(x, X, FUN, ...,
order = is.ordered(x), new.order, sort = SortMixed)factor
auxillary data vector
function to be applied to subsets of X determined by
x, to determine factor order
optional parameters to FUN
logical value indicating whether the returned
object should be an ordered factor
a vector of indexes or a vector of label names giving the order of the new factor levels
function to use to sort the factor level names, used only
when new.order is missing
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.
A new factor with reordered levels
# Create a 4 level example factor
trt <- factor( sample( c("PLACEBO", "300 MG", "600 MG", "1200 MG"),
100, replace=TRUE ) )
summary(trt)
#> 1200 MG 300 MG 600 MG PLACEBO
#> 22 31 22 25
# Note that the levels are not in a meaningful order.
# Change the order to something useful
# default "mixedsort" ordering
trt2 <- reorder(trt)
summary(trt2)
#> 300 MG 600 MG 1200 MG PLACEBO
#> 31 22 22 25
# using indexes:
trt3 <- reorder(trt, new.order=c(4, 2, 3, 1))
summary(trt3)
#> PLACEBO 300 MG 600 MG 1200 MG
#> 25 31 22 22
# using label names:
trt4 <- reorder(trt, new.order=c("PLACEBO", "300 MG", "600 MG", "1200 MG"))
summary(trt4)
#> PLACEBO 300 MG 600 MG 1200 MG
#> 25 31 22 22
# using frequency
trt5 <- reorder(trt, X=as.numeric(trt), FUN=length)
summary(trt5)
#> 1200 MG 600 MG PLACEBO 300 MG
#> 22 22 25 31
# drop out the '300 MG' level
trt6 <- reorder(trt, new.order=c("PLACEBO", "600 MG", "1200 MG"))
summary(trt6)
#> PLACEBO 600 MG 1200 MG NA's
#> 25 22 22 31