On Tue, Jun 16, 2009 at 5:16 AM, Stefan Uhmann <stefan.uhm...@googlemail.com
> wrote:
> 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 tapply is defined for atomic vectors and not for data frames. Why?
I don't know.
Does this do what you want?:
> df <- data.frame(var1 = c(3,2,1), var2 = c(6,5,4), var3 = c(9,8,7))
> fac <- c('a','a','b')
> do.call(rbind, lapply(split(df,fac),mean))
var1 var2 var3
a 2.5 5.5 8.5
b 1.0 4.0 7.0
Alternatively, you can use sapply, which returns the result in matrix form.
> sapply(split(df,fac),mean)
a b
var1 2.5 1
var2 5.5 4
var3 8.5 7
> as.data.frame(t(sapply(split(df,fac),mean)))
var1 var2 var3
a 2.5 5.5 8.5
b 1.0 4.0 7.0
Note that sapply's matrix output form (the so-called 'simplification') needs
to be transposed.
-s
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
