?aggregate will do it.
x <- data.frame( height= c(50, 174, 145, 200, 210, 140, 175),
age_group=c(1,2,2,1,1,2,1),
ville= c(1,2,3,1,2,3,1))
aggregate(x$height,list(x$age_group, x$ville), mean)
or have a look at the plyr or datatable packages.
John Kane
Kingston ON Canada
> -----Original Message-----
> From: skha...@nshs.edu
> Sent: Fri, 16 Nov 2012 15:58:17 -0500
> To: r-help@r-project.org
> Subject: [R] Calculateing means
>
>
> Dear List,
>
> I have a data matrix with 570 columns containing 95 (samples) with 6
> replicates each.
> How can I calculate the mean of the replicates for 95 samples?
> Thank you.
>
>
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