Hi > The plyr solution is: > > library(plyr) > ddply(dfx, .(group, time), summarize, mean = mean(value), sd = sd(value))
I tried to do the task by ddply but I had difficulties to understand the correct syntax. Maybe in next issue of plyr summarise could be referenced in ddply help page. Or add something like: When performing summary values for a data frame according to levels of a factor you shall use syntax ddply(.data, .variables, summarise, .fun, ...) Regards Petr > > 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.