R Language Date-time classes (POSIXct and POSIXlt) Parsing strings into date-time objects
Example
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.
Notes
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
tzparameter, the local timezone is used.
Time zones
- The accepted values of
tzdepend on the location.CSTis given with"CST6CDT"or"America/Chicago"
- For supported locations and time zones use:
- In R:
OlsonNames() - Alternatively, try in R:
system("cat $R_HOME/share/zoneinfo/zone.tab")
- In R:
- These locations are given by Internet Assigned Numbers Authority (IANA)
