reorder.factor {gregmisc}R Documentation

Reorder the Levels of a Factor

Description

Reorder the levels of a factor

Usage

## S3 method for class 'factor':
reorder(x, order, ...)

Arguments

x factor.
order Vector of indexes or label names for new factor ordering.
... Optional parameters (ignored.)

Details

When order is a numeric vector, this function is simply a convenence wrapper for factor(x,levels=levels(x)[order]). Otherwise this functionis simply a wrapper for factor(x,levels=order).

I find this function useful for reordering factors so that the default treatment contrasts use the appropriate levels for comparison.

Value

A new factor with the levels ordered as specified. Note that levels not specified order will become missing values.

Author(s)

Gregory R. Warnes Gregory_R_Warnes@groton.pfizer.com

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
   # using indexes:
   trt2 <- reorder(trt, c(4,2,3,1))
   summary(trt2)
   # using label names:
   trt2 <- reorder(trt, c("PLACEBO","300 MG", "600 MG", "1200 MG") )
   summary(trt2)

   # drop out the '300 MG' level
   trt3 <- reorder(trt, c("PLACEBO", "600 MG", "1200 MG") )
   summary(trt3)
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