Working with dates

d1 = date()
d1

[1] "Sun Jan 12 17:48:33 2014"

class(d1)

[1] "character"

d2 = Sys.Date()
d2

[1] "2014-01-12"

class(d2)

[1] "Date"

%d = day as number (0-31), %a = abbreviated weekday,%A = unabbreviated weekday, %m = month (00-12), %b = abbreviated month, %B = unabbrevidated month, %y = 2 digit year, %Y = four digit year

format(d2,"%a %b %d")

[1] "Sun Jan 12"

x = c("1jan1960", "2jan1960", "31mar1960", "30jul1960"); z = as.Date(x, "%d%b%Y")
z

[1] "1960-01-01" "1960-01-02" "1960-03-31" "1960-07-30"

z[1] - z[2]

Time difference of -1 days

as.numeric(z[1]-z[2])

[1] -1

weekdays(d2)

[1] "Sunday"

months(d2)

[1] "January"

julian(d2)

[1] 16082
attr(,"origin")
[1] "1970-01-01"

library(lubridate); ymd("20140108")

[1] "2014-01-08 UTC"

mdy("08/04/2013")

[1] "2013-08-04 UTC"

dmy("03-04-2013")

[1] "2013-04-03 UTC"

http://www.r-statistics.com/2012/03/do-more-with-dates-and-times-in-r-with-lubridate-1-1-0/

ymd_hms("2011-08-03 10:15:03")

[1] "2011-08-03 10:15:03 UTC"

ymd_hms("2011-08-03 10:15:03",tz="Pacific/Auckland")

[1] "2011-08-03 10:15:03 NZST"

?Sys.timezone

http://www.r-statistics.com/2012/03/do-more-with-dates-and-times-in-r-with-lubridate-1-1-0/

x = dmy(c("1jan2013", "2jan2013", "31mar2013", "30jul2013"))
wday(x[1])

[1] 3

wday(x[1],label=TRUE)

[1] Tues
Levels: Sun < Mon < Tues < Wed < Thurs < Fri < Sat

• More information in this nice lubridate tutorial http://www.r-statistics.com/2012/03/do-more-with-dates-and-times-in-r-with-lubridate-1-1-0/
• The lubridate vignette is the same content http://cran.r-project.org/web/packages/lubridate/vignettes/lubridate.html
• Ultimately you want your dates and times as class "Date" or the classes "POSIXct", "POSIXlt". For more information type ?POSIXlt