On 4/8/2008 5:14 AM, Manuel Montes wrote:
> Does anyone have something like tapply for matrices? I would like to average
> the contents of columns
> according to factors but tapply works only with one column at each time. Is
> something available to do
> everything in one step?
> Many thanks.
> Manuel Montes
How about aggregate()? For example:
aggregate(iris[,c("Sepal.Length", "Sepal.Width", "Petal.Length",
"Petal.Width")], by = list(Species = iris$Species), FUN = mean)
Species Sepal.Length Sepal.Width Petal.Length Petal.Width
1 setosa 5.006 3.428 1.462 0.246
2 versicolor 5.936 2.770 4.260 1.326
3 virginica 6.588 2.974 5.552 2.026
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