Stefan Uhmann wrote:
> Dear List,
>
> why does this not work?
>
> df <- data.frame(var1 = c(3,2,1), var2 = c(6,5,4), var3 = c(9,8,7),
> fac = c('A', 'A', 'B'))
> tapply(cbind(df$var1, df$var2, df$var3), df$fac, mean)
because
length(cbind(df$var1, df$var2, df$var3))
# 9
length(df$fac)
# 3
and that's enough for it not to work, as far as i understand what
?tapply says.
here's another question: why this *does* work (or "work"):
d = data.frame(a=1:3, b=1:3, c=1:3)
f = factor(1:3)
tapply(d, f, c)
# no issues
although
is.atomic(d)
# FALSE
and ?tapply says:
" X: an atomic object, typically a vector."
note the 'atomic'.
vQ
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