There is a problem with tapply() in the case where INDEX is a factor
with at least one of its levels not occurring in it.
In this case,
namelist[[i]] <- levels(index)
gets all levels but
group <- group + ngroup * (codes(index) - 1)
only those occurring in index, which subsequently causes
names(ans) <- namelist[[1]]
to fail.
For example,
R> f <- factor(c("a", "a", "b"), levels =
letters[1:3])
R> f
[1] a a b
R> codes(f)
[1] 1 1 2
R> levels(f)
[1] "a" "b" "c"
which gives e.g.
R> tapply(rep(1, length(f)), f, sum)
Error: names attribute must be the same length as the vector
One solution is to replace
namelist[[i]] <- levels(index)
by
namelist[[i]] <- unique(levels(index)[index])
but perhaps there is something smarter ...
-k
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