Reorder the Levels of a Factor

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Description

Reorder the levels of a factor

Usage

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

Arguments

x

factor

X

auxillary data vector

FUN

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

Value

A new factor with reordered levels

Author(s)

Gregory R. Warnes greg@warnes.net

See Also

factor and reorder

Examples

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   # 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=rnorm(100), FUN=mean)
   summary(trt5)

   # Drop out the '300 MG' level
   trt6 <- reorder(trt, new.order=c("PLACEBO", "600 MG", "1200 MG"))
   summary(trt6)

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