If I have a data frame something like: Value=rnorm(30) Group = sample(c('A','B','C'), 30, replace=TRUE) df = data.frame(Value, Group)
It seems like it should be simple to create an 'ObsID' column which indicates the observation order of each Value within each of the 3 groups. Somehow, I can't quite see how to do it without manually sub-setting the parent data frame and then putting it back together again. Anyone able to get me started on a cleaner (more R-like) approach? Thanks, Rob ------------------------------------------ Robert W. Baer, Ph.D. Professor of Physiology Kirksville College of Osteopathic Medicine A. T. Still University of Health Sciences 800 W. Jefferson St. Kirksville, MO 63501 660-626-2322 FAX 660-626-2965 [[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.