On 08-Jul-08 13:18:13, Daniela Ottaviani wrote: > 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.
I think something on the following lines would do what you want (I think it is wise to call the final column "Pr.mean", as below, rather than "Pr_mean"): for( Code in unique(myD$code) ){ ix <- (myD$code == Code ) myD$Pr.mean[ix] <- mean(myD$prevalence[ix]) } Ted. > 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. -------------------------------------------------------------------- E-Mail: (Ted Harding) <[EMAIL PROTECTED]> Fax-to-email: +44 (0)870 094 0861 Date: 08-Jul-08 Time: 17:01:38 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.