[R] Expand DF with all levels of a variable

[Dimitris Rizopoulos]

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

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