Hi R Users, I'm wondering how can I calculate two (or three) way sum of a variable. A sample data is:
State Month Year Value NC Jan 1996 1 NC Jan 1996 2 NC Feb 1997 2 NC Feb 1997 3 NC Mar 1998 3 NC Mar 1998 4 NY Jan 1996 4 NY Jan 1996 5 NY Feb 1997 5 NY Feb 1997 6 NY Mar 1998 6 NY Mar 1998 7 I'm trying to sum up "value" column by State*Month and by State*Month*Year. Also, I may need to calculate mean value along with "sum". Any help would be greatly appreciated, Thanks, Peng [[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.