On May 26, 2011, at 10:04 AM, Mikkel Grum wrote: > Thanks Marc, > > I had just come up with another, slightly more convoluted solution. Add as.is > = TRUE to the query and then get the timetoken with > timetoken <- df$timestamp[df$timestamp == max(as.POSIX(df$timestamp))] > > While it looks like options(digits.secs = 6) works, I worry that > theoretically it just pushes the problem down to another level of decimal > points. With the solution above, I apparently get the exact same value that > was in the database. > > Interestingly, > timetoken <- max(as.POSIX(df$timestamp)) > does not appear to give me the same result. > > Demo: >> a <- "2011-05-25 22:15:11.027116000" >> b <- "2011-05-25 22:15:11.027117000" >> c <- "2011-05-25 22:15:11.027118000" >> d <- c(a, b, c) >> d > [1] "2011-05-25 22:15:11.027116000" "2011-05-25 22:15:11.027117000" > "2011-05-25 22:15:11.027118000" >> d[d == max(as.POSIXct(d))] > [1] "2011-05-25 22:15:11.027118000" >> max(as.POSIXct(d)) > [1] "2011-05-25 22:15:11 COT"
Hi Mikkel, >From what I can tell, PostgreSQL stores timestamp data with millisecond >precision: http://wiki.postgresql.org/wiki/Working_with_Dates_and_Times_in_PostgreSQL So 6 decimal place precision in R should be more than sufficient. You have a similar problem in your last example here: # This is returning the indexed value in the original character vector 'd' # not the coerced POSIXct object. So you get the original quoted string, # including the irrelevant trailing 0's > d[d == max(as.POSIXct(d))] [1] "2011-05-25 22:15:11.027118000" # Now you are printing POSIXct objects, which have the same limitation as I raised earlier: > max(as.POSIXct(d)) [1] "2011-05-25 22:15:11 CDT" options(digits.secs = 6) > max(as.POSIXct(d)) [1] "2011-05-25 22:15:11.027118 CDT" This is the classic problem of differentiating between how R is storing the data internally and how R *prints* the data to the console via various default formatting options. Regards, Marc ______________________________________________ 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 and provide commented, minimal, self-contained, reproducible code.
