Try: > myD <- transform(myD, Pr_mean = ave(prevalence, codes))
See ?ave and ?transform for details. -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Daniela Ottaviani > Sent: Tuesday, July 08, 2008 7:18 AM > To: r-help@r-project.org > Subject: [R] Question: Beginner stuck in a R cycle > > Dear All, > > I have a database of 200 observations named myD. > In the dataframe there are a column named code (with codes > varying from 1 to 77), a column named "prevalence" with some > quantitative measurements are given and an column named > Pr_mean, with no values. > > I would like to set a cycle to compute the average of > prevalence values for each different code and store the > averages under the empty field Pr_mean. > > This is what I wrote: > > # Set a cycle > for (i in 1:nrow(myD)) { > mycode = myD$code[i] > mymean[i] = mean(prevalence) > myD$Pr_mean[i] = mymean[i] > } > > With the above cycle I am able to compute the average of all > 200 observations which is then written in every cell. > I understand that a condition is missing, that indicates that > the average has to be computed amongst the observations > showing the same codes values. > > Could you please help me ? > > > D. > > > > Posta, news, sport, oroscopo: tutto in una sola pagina. > Crea l'home page che piace a te! > www.yahoo.it/latuapagina > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@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. > ______________________________________________ R-help@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.
