rockchalk (version 1.8.157)

combineLevels: recode a factor by "combining" levels

Description

This makes it easy to put levels together and create a new factor variable. 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! This is a surprisingly difficult problem in R.

Usage

combineLevels(fac, levs, newLabel = "combinedLevels")

Value

A new factor variable, with unused levels removed.

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 spelled* factor values, such as c("Yes","Maybe","Always") or it may be provided as a subset of the output from levels, such as levels(fac)[1:3].

newLabel

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

Author

Paul E. Johnson

Details

If the factor is an ordinal factor, then levels may be combined only if they are adjacent. 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))