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
try this:
mat <- matrix(rnorm(1000), 100, 10)
ind <- gl(4, 25)
rowsum(mat, ind) / rep(table(ind), each = ncol(mat))
I hope it helps.
Best,
Dimitris
----
Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
http://www.student.kuleuven.be/~m0390867/dimitris.htm
----- Original Message -----
From: "Manuel Montes" <jmmontes at uni-hohenheim.de>
To: <r-help at r-project.org>
Sent: Tuesday, April 08, 2008 11:14 AM
Subject: [R] tapply
> 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
>
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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 MontesHow 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> ______________________________________________ > R-help at 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.-- Chuck Cleland, Ph.D. NDRI, Inc. (www.ndri.org) 71 West 23rd Street, 8th floor New York, NY 10010 tel: (212) 845-4495 (Tu, Th) tel: (732) 512-0171 (M, W, F) fax: (917) 438-0894