rockchalk (version 1.6.2)

combineLevels: recode a factor by "combining" levels

Description

If a factor variable is currently coded with levels c("Male","Female","Man", "M"), and the user needs to combine the redundant levels for males, this is the function to use!

Usage

combineLevels(fac, levs, newLabel)

Arguments

fac

An R factor variable, either ordered or not.

levs

The levels to be combined. Users may specify either a numerical vector of level values, such as c(1,2,3), to combine the first three elements of level(fac), or they may specify level names. This can be done as a character vector of *correctly spe

newLabel

A character string that represents the label of the new level to be created when levs values are combined.

Value

• A new factor variable, with unused levels removed.

Details

If the factor is an ordinal factor, then levels may be combined only if they are adjacent. That is to say, a factor with levels c("Lo","Med","Hi","Extreme") allows us to combine responses "Lo" and "Med", while it will NOT allow us to combine "Lo" with "Hi".

A non-ordered factor can be reorganized to combine any values, no matter what positions they occupy in the levels vector.

Examples

x <- c("M","A","B","C","A","B","A","M")
x <- factor(x)
levels(x)
x2a <- combineLevels(x, levs = c("M","A"), newLabel = "M_or_A")
addmargins(table(x2a, x, exclude=NULL))
x2b <- combineLevels(x, c(1,4), "M_or_A")
addmargins(table(x2b, x, exclude=NULL))
x3 <- combineLevels(x, levs = c("M","A","C"), newLabel = "MAC")
addmargins(table(x3, x, exclude=NULL))
## Now an ordinal factor
z <- c("M","A","B","C","A","B","A","M")
z <- ordered(z)
levels(z)
table(z, exclude=NULL)
z2a <-  combineLevels(z, levs = c(1,2), "Good")
addmargins(table(z2a, z, exclude = NULL))
z2b <- combineLevels(z, levs = c("A","B"), "AorB")
addmargins(table(z2b, z, exclude = NULL))
## Should fail:
## z2 <- combineLevels(z, levs=c("A","C"), "Whoops!")