I have been trying to figure out how Hadley Wickhams "reshape" package works and I tried it on what may be your problem. Here is my example. Does it do something like what you want? =============================================== # Test Data zz <- "subj cond t1 t2 t3 A 1 4 5 7 A 2 5 2 8 B 2 3 7 3 C 1 5 4 4 B 1 4 5 5 C 2 3 7 7" mydata <- read.table(textConnection(zz), header=TRUE, as.is=TRUE); mydata
library(reshape) # Melt the data.frame df1 <- melt(mydata, id=c("subj", "cond"), measured=c("t1","t2","t3")) ; df1 # calculate the mean and sd stats <- cast(df1, subj + cond ~ . , function(x) c(mean= mean(x), sd=sd(x))) # Merge the original data.frame and the stats data.frame to get the # desired results. combined.results <- merge(mydata,stats, by=c("subj","cond")); combined.results ================================================= --- 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? Perhaps a random word generator? > > Thanks, > Dieter Vanderelst ______________________________________________ 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.