here is a solution with expand.grid(),

a <- c(2,2,3,4,5,6,7,8,9)
a.cut <- cut(a, breaks=c(0,2,6,9,12,13,15,16), right=FALSE )
x <- data.frame(a, a.cut)

out <- expand.grid(a = 0, a.cut = setdiff(levels(a.cut), unique(a.cut)))
rbind(out, x)


I hope it helps.

Best,
Dimitris



On 6/14/2011 1:32 PM, Patrick Hausmann wrote:
Dear list,

I would like to expand a DF with all the missing levels of a variable.

a <- c(2,2,3,4,5,6,7,8,9)
a.cut <- cut(a, breaks=c(0,2,6,9,12), right=FALSE )
(x <- data.frame(a, a.cut))

# In 'x' the level "[0,2)" is "missing".

AddMissingLevel <- function(xdf) {

xfac <- factor( c("[0,2)", "[2,6)", "[6,9)", "[9,12)") )
xlevels <- levels(xfac)

if(length(xlevels) != nlevels(factor(xdf$a.cut))) {
v <- setdiff(xlevels, factor(xdf$a.cut))
u <- data.frame(a = 0, a.cut = v)
x <- rbind(u, x)
}
return(x)
}

AddMissingLevel(x)

Does a more general approach exist, e.g. using "expand.grid"?

Thanks for any help!!
Patrick

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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
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