Paul Sorenson <Paul.Sorenson <at> vision-bio.com> writes: : : I have a frame which contains 3 columns: : : "date" "defectnum" "state" : : And I want to get the most recent state change for a given defect number. date is POSIXct. : : I have tried: : aggregate(ev$date, by=list(ev$defectnum), max) : : Which appears to be working except that the dates seem to come back as integers (presumably the internal : representation of POSIXct). : : When I execute max(ev$date) the result remains POSIXct. : : I have been dredging through the help among DateTimeClasses and haven't found a function that converts : these integers to some kind of date class. Or a method for using aggregate
RNews 4/1 has an article with this and other date conversions. : which doesn't perform the : conversion in the first place. You could sort ev by date and use aggregate on an index vector (untested): ev <- ev[order(ev$date),] ev[aggregate(1:nrow(ev), list(ev$defectnum), max),] ______________________________________________ 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