Liaw, Andy wrote:
Suppose I define the function:
fun <- function(x, f) { m <- tapply(x, f, mean) ans <- x - m[match(f, unique(f))] names(ans) <- names(x) ans }
May I ask what is the purpose of match(f,unique(f)) ?
To remove the group means, I have be using:
x-tapply(x,f,mean)[f]
for a while, (and I am now changing to x-tapply(x,f,mean)[as.character(f)] because of the peculiarities of indexing named vectors with factors )
The use of tapply(x,f,mean)[match(f,unique(f))] assumes a particular order in the result of tapply, no? It seems a bit dangerous to me.
Christophe Pallier
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