On Monday, October 22, 2012, nymphita wrote: > Hello all, > I'm trying to group several consecutives rows (and assigning them the same > value) while leaving some of the rows empty (when a certain condition is > not > fulfilled). > > My data are locations (xy coordinates), the date/time at which they were > measured, and the time span between measures. Somehow simplified, they look > like this: > > > > I'd like to assign a value to every sequence of locations that are measured > within a time span of 4 hours, and make my data look like this: > > > > I've tried several algorithms with a loop "for" plus "ifelse" condition > like: > > Sequence <- for (i in 1:max(ID)) { > ifelse (Span <= 4, i+1, "NA") > } Very rarely is the output of a `for` loop (used that way) useful. I'd recommend you take 15 minutes to reread the sections on vectorization and control structures in the introductory manual which ships with R. To get at it, type help.start() at the prompt. I _think_ you want something like the following in this case, but the question isn't entirely clear to me. Cheers, Michael sequence <- seq_along(Span) is.na(sequence) <- Span > 5 > > > without any luck. I know my attempt is incorrect, but my programming skills > are really basic and I haven't found any similar problem in the web. > > Any ideas would be very appreciated! > > > > -- > View this message in context: > http://r.789695.n4.nabble.com/Assigning-values-to-several-consecutives-rows-in-a-sequence-while-leaving-some-empty-tp4646956.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 > seq > > > > > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]]