Look at ?tapply, based on your description, it is what you want. Ben
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ng Stanley Sent: Thursday, March 13, 2008 9:25 AM To: r-help Subject: [PS] [R] How to manipulate data according to groups ? Hi, I have a two columns data, the first column are values, and second column are the groups. For this example, there are 3 groups 1,2,3. How can I manipulate the values in the first column according to groups, say I would like to find mean, sum, and standard deviation for the different groups ? How do I plot data according to groups ? > t <- matrix(c(rnorm(10), 1,1,2,2,1,3,3,3,3,2), ncol=2) [[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. ______________________________________________ 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.
