Does this do what you want? > x <- data.frame(subj=sample(1:3,20,TRUE), cond=sample(1:2,20,TRUE), > time=runif(20,1,10)) > # add mean and sd > x$mean <- ave(x$time, x$subj, x$cond) > x$sd <- ave(x$time, x$subj, x$cond, FUN=sd) > x subj cond time mean sd 1 3 2 3.563114 5.637710 2.879756 2 2 2 9.055847 6.641738 2.051851 3 2 1 5.016118 5.955314 2.777777 4 1 1 8.019864 8.079528 0.598062 5 3 2 8.925571 5.637710 2.879756 6 2 1 4.718118 5.955314 2.777777 7 2 1 1.574276 5.955314 2.777777 8 1 2 4.019387 6.292459 3.214609 9 1 1 7.513534 8.079528 0.598062 10 2 2 4.038538 6.641738 2.051851 11 2 2 6.673727 6.641738 2.051851 12 1 2 8.565531 6.292459 3.214609 13 1 1 8.705185 8.079528 0.598062 14 2 1 4.522234 5.955314 2.777777 15 3 2 4.424445 5.637710 2.879756 16 2 1 9.059009 5.955314 2.777777 17 2 2 6.798842 6.641738 2.051851 18 2 1 7.669708 5.955314 2.777777 19 3 1 6.447731 6.447731 NA 20 2 1 9.127735 5.955314 2.777777
On 10/19/07, Dieter Vanderelst <[EMAIL PROTECTED]> wrote: > Dear List, > > I have a data frame containing reaction times of participants in some > experiment. > > As usual each line is single trial in the experiment. Two factors denote the > conditions in the experiment. Each participant completes different trials for > each condition. > > Now, the question: > > I want to calculate per participant, per condition the mean reaction time and > its standard deviation. > > I can do this using AGGREGATE(). However, I want to merge this info with the > original data frame. This is, I want each line to contain the mean and SD of > the reaction time for the participant and condition on that line. > > I have tried to solve this by looping trough data frame. For each line, I > select using SUBSET() the lines that belong to the same participant and > condition. Then I calculate the average/SD. But this takes a long time. > > BYTW: I find that finding proper subject for r-help list mails, is very hard. > So, if any one knows a set of better keywords... > > Any ideas? > > Thanks, > Dieter Vanderelst > > ------------------------------------------ > Dieter Vanderelst > > dieter _ vanderelst AT emailengine DOT org > d DOT vanderelst AT tue DOT nl > > Eindhoven University of Technology > Faculty of Industrial Design > Designed Intelligence Group > Den Dolech 2 > 5612 AZ Eindhoven > The Netherlands > Tel +31 40 247 91 11 > > ______________________________________________ > 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. > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem you are trying to solve? ______________________________________________ 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.