Re: [R] Two basic data manipulation questions (counting and	aggregating) Hi, Sorry for replying to myself, but I think I have found a solution for my first question. > First, I would like to create a "counter" variable which will count > the rank of each row inside each "id" level, ie something like : > > id     type   counter > 10002  "7"      1  > 10061  "1"      1 > 10061  "1"      2 > 10061  "4"      3 > 10065  "7"      1 > 10114  "1"      1  > 10114  "1"      2 > 10114  "4"      3 > 10136  "7"      1 > 10136  "2"      2 > 10136  "2"      3 If I use : df$counter <- unlist(tapply(df$id, df$id, order)) But there may be a better solution... --  Julien ______________________________________________ R-help@stat.math.ethz.ch 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.