[R] Re: coding factor replicates

[Peter Dalgaard BSA]

Douglas Bates <bates at stat.wisc.edu> writes:

> I would do it as
> 
> > result <- seq(along = f)         # create an vector to hold the response
> > sp <- split(seq(along = f), f)   # split the factor on levels
> > result[unlist(sp)] <- unlist(lapply(sp, function(x) seq(along = x)))
> > result
>  [1] 1 1 1 2 2 2 3 3 3 4 4
> 
> but I'm sure Bill would do it much more elegantly than that.

Essentially the same thing, but we saw a similar pattern recently and
I wonder whether we should systematize it:

"split<-" <- function(x,f,value){
    x[unlist(split(seq(along=x),f)] <- unlist(value)
    x
}

unsplit <- function(v,f) {
    x <- vector(length=length(f))
    split(x,f) <- v
    x
}

Now we can do (breaks horribly if there's an empty factor level, though):

unsplit(lapply(table(f), seq)))

and the within-group z-score from the other day would become

unsplit(tapply(x,f,scale),f)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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