The plyr solution is: library(plyr) ddply(dfx, .(group, time), summarize, mean = mean(value), sd = sd(value))
Best, Ista On Wed, Aug 31, 2011 at 7:13 AM, Petr PIKAL <petr.pi...@precheza.cz> wrote: > Hi > >> Hi all, >> I apologize for this probably stupid question, but I really can't figure > it >> out. >> I have a dataframe like this: >> >> group <- c(rep('A', 8), rep('B', 15), rep('C', 6)) >> time <- c(rep(seq(1:4), 2), rep(seq(1:5), 3), rep(seq(1:3), 2)) >> value <- runif (29, 1, 10) >> dfx <- data.frame (group, time, value) >> >> I want to calculate mean and standard deviation for all values that > belong >> to the same group and the same time and end up with a dataframe with the >> columns time, group, mean and sd that contains the calculated values for >> every group at every time point only once (12). >> What is the most elegant way to do this? Oh, and I would like to avoid >> renaming columns (like the _X1/_X2 created by casting with multiple >> functions), if possible. >> I am sure that this is pretty basic, but I have already wasted a > ridiculous >> amount of time on this. > > see > ?aggregate > > aggregate(dfx$value, list(group=dfx$group, time=dfx$time), function(x) > c(mean(x), sd(x))) > > and maybe also plyr package could help you > > Regards > Petr > > >> >> Thanks, >> >> Kai >> >> [[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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.