reorder.RdReorder the levels of a factor
# S3 method for class 'factor'
reorder(x, X, FUN, ..., order=is.ordered(x), new.order, sort=mixedsort)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 a numeric vector, the new factor level names
are constructed by reordering the factor levels according to the
numeric values. If new.order is a chraccter vector,
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 calling the function specified by sort
to the existing factor level names. With sort=mixedsort
(the default) 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
#> 28 34 25 13
# 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
#> 34 25 28 13
# - using indexes:
trt3 <- reorder(trt, new.order=c(4, 2, 3, 1))
summary(trt3)
#> PLACEBO 300 MG 600 MG 1200 MG
#> 13 34 25 28
# - 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
#> 13 34 25 28
# - using frequency
trt5 <- reorder(trt, X=rnorm(100), FUN=mean)
summary(trt5)
#> 300 MG 600 MG 1200 MG PLACEBO
#> 34 25 28 13
# 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
#> 13 25 28 34