[R] tapply

[Dimitris Rizopoulos]

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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