I have a data frame containing children, with variables 'year' = birth year, and 'm.id' = mother's id number. Let's assume that all the births of each mother is represented in the data frame.
Now I want to create a subset of this data frame containing all children, whose mother's first birth was in the year 1816 or later. This seems to work: mid <- tapply(dat$year, dat$m.id, min) mid <- as.numeric(names(mid)[mid >= 1816]) dat <- dat[dat$m.id %in% mid, ] but I'm worried about the second line, because the output from 'tapply' isn't documented to have a 'dimnames' attribute (although it has one, at least in R-2.1.0, 2005-01-19). Another aspect is that this code relies on m.id being numeric; I would have to change it if the type of m.id changes to, eg, character. So, question: Is there a better way of doing this? -- Göran Broström tel: +46 90 786 5223 Department of Statistics fax: +46 90 786 6614 Umeå University http://www.stat.umu.se/egna/gb/ SE-90187 Umeå, Sweden e-mail: [EMAIL PROTECTED] ______________________________________________ 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