I had the same error "Error in as.ltraj(xy, id, date = da) : non unique dates for a given burst", but from a different cause, that I'd like to share in case others have the same issue.
My data came from GPS collars that collected dates and time in Greenwich Mean Time (GMT). However, the package automatically uses time appropriate for your local area. My data had been collected during October when Australia switches from standard time to summer time. Thus the times 0200h and 0230h on 6 October did not exist and were perceived as 'non unique dates' between 0100h AEST and 0300h AEDT. This can easily be fixed by specifying the time zone when extracting the dates using as.POSIXct GPSdata$datetime <- (strptime(paste(GPSdata$Date, GPSdata$Time), "%Y %m %d %H:%M:%S")) GPSdata$datetime <- as.character(GPSdata$datetime) when <- as.POSIXct(GPSdata$datetime, tz="GMT") foxdata <- as.ltraj(xy = GPSdata[,c("North.", "East.")], date = when, id = GPSdata$Animal) Bronwyn Hradsky Department of Forest & Ecosystem Science University of Melbourne -- View this message in context: http://r.789695.n4.nabble.com/Duplicated-date-values-aren-t-duplicates-tp897178p4701489.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.