gdata (version 2.2.0)

reorder.factor: Reorder the Levels of a Factor

Description

Reorder the levels of a factor

Usage

## S3 method for class 'factor':
reorder(x,
                         order,
                         X,
                         FUN,
                         sort=mixedsort,
                         make.ordered = is.ordered(x),
                         ... )

Arguments

x

factor.

order

A vector of indexes or a vector of label names giving the order of the new factor levels.

X

auxillary data vector

FUN

function to be applied to subsets of X determined by x, to determine factor order.

sort

function to use to sort the factor level names

make.ordered

logical value indicating whether the returned object should be an 'ordered' factor.

...

Optional parameters to FUN.

Value

• A new factor with the levels ordered as specified.

Details

This function changes the order of the levels of a factor. It can do so via three different mechanisms, depending on whether order, X and FUN, or sort are provided.

If 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, order gives the list of new factor level names. In either case levels omitted from order will become missing values.

If X and Fun are provided: The data in X is grouped by the levels of data 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 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 order="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 be numeric rules for the numeric sections. See mixedsort for details.

See Also

factor, reorder

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, c(4,2,3,1))
   summary(trt3)
   # using label names:
   trt4 <- reorder(trt, 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, c("PLACEBO", "600 MG", "1200 MG") )
   summary(trt6)