R Programming/Times and Dates

R contains a set of object types for holding date and time information. The system time and date can also be requested.

Format

Many time and date units are recognised. These include:

Unit	Symbol	Example
4 digit year	%Y	1932
2 digit year	%y	84
Numerical Month	%m	03
Full Month	%B	January
Abbreviated Month	%b	Jan
Day of the month	%d	31
Full weekday	%A	Wednesday
Abbreviated weekday	%a	Wed
Hours (24hr clock)	%H	16
Minutes	%M	35
Seconds	%S	52

The default format is yyyy-mm-dd hh:mm:ss or %Y-%m-%d %H:%M:%S

For example 2010-02-13 23:12:24

System Date and Time

To get the system date and time:

> Sys.time()
 [1] "2010-02-13 23:12:24 COT"
> format(Sys.time(),"%H %M")   # in a different format and without the date
 [1] "23 13"
> Sys.date()
 [1] "2010-02-13"
> date()                       # returns the current date and time,
[1] "Wed Jul 18 10:59:42 2012"

Convert Strings to Date/Time Objects

Convert a string representing the date or time into a Date/Time object:

> my.date <- as.Date("2010-12-20")
> print(my.date)
 [1] "2011-12-30"
> my.date2 <- as.Date("12/20/10", format="%m/%d/%y") # input date in a different format
> print(my.date2)
 [1] "2010-12-30"
> my.time <- strptime("12/20/10 14.34.35", format="%m/%d/%y %H.%M.%S") # input time and date
> print(my.time)
 [1] "2010-12-30 14:34:35"
> my.string <- as.character(Sys.time()) # convert a date/time object to a normal string
> print(my.string)
 [1] "2011-02-30 02:31:15"

Most Useful Utility Functions for Dates

Get weekday, month and an integer representing the number of days since the beginning of epoch:

> weekdays(my.date) # Get a string representing the weekday of the specified date
[1] "Monday"
> months(my.date)
[1] "December" # Get the month as well
> my.date
[1] "2010-12-20"
> julian(my.date) # Get the integer number of days since the beginning of epoch
[1] 14963
attr(,"origin")
[1] "1970-01-01"

External links

• Do more with dates and times in R with lubridate 1.1.0 (a sample chapter from the “R in Action” book)