Accurately converting from character->POSIXct->character with sub millisecond datetimes

Question

I have a character datetime column in a file. I load the file (into a data.table) and do things that require the column to be converted to POSIXct.

Answer 1

As the answers to the questions you linked to already say, how a value is printed/formatted is not the same as what the actual value is. This is just a printed representation issue.

R> as.POSIXct('2011-10-11 07:49:36.3')-as.POSIXlt('2011-10-11 07:49:36.3')
Time difference of 0 secs
R> as.POSIXct('2011-10-11 07:49:36.2')-as.POSIXlt('2011-10-11 07:49:36.3')
Time difference of -0.0999999 secs

Your understanding that POSIXct is less precise than POSIXlt is incorrect. You're also incorrect in saying that you can't include a POSIXlt object as a column in a data.frame.

R> x <- data.frame(date=Sys.time())
R> x$date <- as.POSIXlt(x$date)
R> str(x)
'data.frame':   1 obs. of  1 variable:
 $ date: POSIXlt, format: "2013-03-13 07:38:48"