Factor Codes

Description

This (generic) function returns a numeric coding of a factor. It can also be used to assign to a factor using the coded form.

Usage

codes(x)
codes(x) <- value

Value

For an ordered factor, it returns the internal coding (1 for the lowest group, 2 for the second lowest, etc.).

For an unordered factor, an alphabetical ordering of the levels is assumed, i.e the level that is coded 1 is the one whose name is sorted first according to the prevailing collating sequence. Warning: the sort order may well depend on the locale, and should not be assumed to be ASCII.

Note

Normally codes is not the appropriate function to use with an unordered factor. Use unclass or as.numeric to extract the codes used in the internal representation of the factor, as these do not assume that the codes are sorted.

Note

The behaviour for unordered factors is dubious, but compatible with S version 3. To get the internal coding of a factor, use as.integer. Note in particular that the codes may not be the same in different language locales because of collating differences.

See Also

factor, levels, nlevels.

Examples

codes(rep(factor(c(20,10)),3))

x <- gl(3,5)
codes(x)[3] <- 2
x

data(esoph)
( ag <- esoph$alcgp[12:1] )
codes(ag)

codes(factor(1:10)) # BEWARE!