I also don't understand, but perhaps: with(df, tapply(aps, list(class, id), mean))
-- Henrique Dallazuanna Curitiba-Paraná-Brasil 25° 25' 40" S 49° 16' 22" O On 19/07/07, sigalit mangut-leiba <[EMAIL PROTECTED]> wrote: > hello, > i want to compute the mean of a variable ("aps") for every class > (1,2, and 3). > every id have a few obs., "aps" and class are constant over id. > like this: > id aps class > 1 11 2 > 1 11 2 > 1 11 2 > 1 11 2 > 1 11 2 > 2 8 3 > 2 8 3 > 2 8 3 > 3 12 2 > 3 12 2 > . > . > > i tried: > > tapply(icu1$aps_st, icu1$hidclass, function(z) mean(unique(z))) > > but it's counting every row and not every id. > > thank you, > > Sigalit. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > ______________________________________________ R-help@stat.math.ethz.ch 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.