R: Reorder the Levels of a Factor

reorder.factor {gdata} | R Documentation

## Reorder the Levels of a Factor

### Description

Reorder the levels of a factor

### Usage

    ## 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

       # 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)

[Package gdata version 2.18.0 Index]