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)
Thank you,
Stefan
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