Hi Christopher, i think you have the same problem like me today :) see this http://r.789695.n4.nabble.com/group-by-in-data-frame-tc3324240.html post i think you can find there the solution
zem -- View this message in context: http://r.789695.n4.nabble.com/means-SD-s-and-tapply-tp3325158p3325191.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ [email protected] 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.
