The help says
A data frame is split by row into data frames subsetted by the
values of one or more factors, and function 'FUN' is applied to
each subset in turn.
You attempting to apply median() to a data frame -- it does no work,
unlike mean()
On Fri, 2 May 2008, vito muggeo wrote:
dear all,
Could anyone explain me the behaviour of median() within by()?
(I am running R.2.7.0)
thanks,
vito
H<-cbind(rep(0:1,l=20),matrix(rnorm(20*2),20,2))
by(H[,-1],H[,1],mean)
INDICES: 0
V1 V2
-0.2101069 0.2954377
---------------------------------------------------------------------------------------------------------------------
INDICES: 1
V1 V2
-0.23682173 -0.01225147
by(H[,-1],H[,1],median)
Error in median.default(data[x, , drop = FALSE], ...) : need numeric data
--
====================================
Vito M.R. Muggeo
Dip.to Sc Statist e Matem `Vianelli'
Università di Palermo
viale delle Scienze, edificio 13
90128 Palermo - ITALY
tel: 091 6626240
fax: 091 485726/485612
http://dssm.unipa.it/vmuggeo
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--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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