R Language Date-time classes (POSIXct and POSIXlt) Parsing strings into date-time objects


The functions for parsing a string into POSIXct and POSIXlt take similar parameters and return a similar-looking result, but there are differences in how that date-time is stored; see "Remarks."

as.POSIXct("11:38",                        # time string
           format = "%H:%M")               # formatting string
## [1] "2016-07-21 11:38:00 CDT"           
strptime("11:38",                          # identical, but makes a POSIXlt object
         format = "%H:%M")
## [1] "2016-07-21 11:38:00 CDT"

as.POSIXct("11 AM",                   
           format = "%I %p")        
## [1] "2016-07-21 11:00:00 CDT"

Note that date and timezone are imputed.

as.POSIXct("11:38:22",                 # time string without timezone
           format = "%H:%M:%S",   
           tz = "America/New_York")    # set time zone
## [1] "2016-07-21 11:38:22 EDT"

as.POSIXct("2016-07-21 00:00:00",
           format = "%F %T")           # shortcut tokens for "%Y-%m-%d" and "%H:%M:%S"

See ?strptime for details on the format strings here.


Missing elements

  • If a date element is not supplied, then that from the current date is used.
  • If a time element is not supplied, then that from midnight is used, i.e. 0s.
  • If no timezone is supplied in either the string or the tz parameter, the local timezone is used.

Time zones