Dear all, Probably a rather stupid question, but I couldn't find the answer..
I currently have a dataframe with customers' id's and purchase amount, what I would like to do is to show the difference between amount purchased compared to the month before per customer. I have made some attempts myself using diff, but what i can not get to work is that each different customer starts with a 0. This is an example of what I have: >purchase_amount customer amount 123 6 123 5 123 9 123 8 123 11 123 7 230 19 230 18 230 12 230 17 380 7 380 9 380 2 380 7 380 8 380 8 380 6 380 8 How I would like it to look like: customer amount difference 123 6 0 123 5 -1 123 9 4 123 8 -1 123 11 3 123 7 -4 230 19 0 230 18 -1 230 12 -6 230 17 5 380 7 0 380 9 2 380 2 -7 380 7 5 380 8 1 380 8 0 380 6 -2 380 8 2 I hope my question is clear like this. Many thanks in advance Rens -- View this message in context: http://r.789695.n4.nabble.com/Differences-per-group-tp3343800p3343800.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
