Extract the weekday, month or quarter, or the Julian time (days since some origin). These are generic functions: the methods for the internal date-time classes are documented here.
Usage
# S3 method for class 'time_period'
quarters(x, ...)Value
weekdays and months return a character
vector of names in the locale in use, i.e., Sys.getlocale("LC_TIME").
quarters returns a character vector of "Q1" to
"Q4".
julian returns the number of days (possibly fractional)
since the origin, with the origin as a "origin" attribute.
All time calculations in R are done ignoring leap-seconds.
Note
Other components such as the day of the month or the year are
very easy to compute: just use as.POSIXlt and extract
the relevant component. Alternatively (especially if the components
are desired as character strings), use strftime.
See also
DateTimeClasses, Date;
Sys.getlocale("LC_TIME") crucially for months() and weekdays().
Examples
## first two are locale dependent:
weekdays(.leap.seconds)
#> [1] "Saturday" "Monday" "Tuesday" "Wednesday" "Thursday" "Saturday"
#> [7] "Sunday" "Monday" "Tuesday" "Wednesday" "Thursday" "Friday"
#> [13] "Monday" "Friday" "Monday" "Tuesday" "Wednesday" "Thursday"
#> [19] "Friday" "Monday" "Tuesday" "Friday" "Sunday" "Thursday"
#> [25] "Sunday" "Wednesday" "Sunday"
months (.leap.seconds)
#> [1] "July" "January" "January" "January" "January" "January" "January"
#> [8] "January" "January" "July" "July" "July" "July" "January"
#> [15] "January" "January" "July" "July" "July" "January" "July"
#> [22] "January" "January" "January" "July" "July" "January"
quarters(.leap.seconds)
#> [1] "Q3" "Q1" "Q1" "Q1" "Q1" "Q1" "Q1" "Q1" "Q1" "Q3" "Q3" "Q3" "Q3" "Q1" "Q1"
#> [16] "Q1" "Q3" "Q3" "Q3" "Q1" "Q3" "Q1" "Q1" "Q1" "Q3" "Q3" "Q1"
## Show how easily you get month, day, year, day (of {month, week, yr}), ... :
## (remember to count from 0 (!): mon = 0..11, wday = 0..6, etc !!)
##' Transform (Time-)Date vector to convenient data frame :
dt2df <- function(dt, dName = deparse(substitute(dt))) {
DF <- as.data.frame(unclass(as.POSIXlt( dt )))
`names<-`(cbind(dt, DF, deparse.level=0L), c(dName, names(DF)))
}
## e.g.,
dt2df(.leap.seconds) # date+time
#> .leap.seconds sec min hour mday mon year wday yday isdst zone gmtoff
#> 1 1972-07-01 0 0 0 1 6 72 6 182 0 GMT 0
#> 2 1973-01-01 0 0 0 1 0 73 1 0 0 GMT 0
#> 3 1974-01-01 0 0 0 1 0 74 2 0 0 GMT 0
#> 4 1975-01-01 0 0 0 1 0 75 3 0 0 GMT 0
#> 5 1976-01-01 0 0 0 1 0 76 4 0 0 GMT 0
#> 6 1977-01-01 0 0 0 1 0 77 6 0 0 GMT 0
#> 7 1978-01-01 0 0 0 1 0 78 0 0 0 GMT 0
#> 8 1979-01-01 0 0 0 1 0 79 1 0 0 GMT 0
#> 9 1980-01-01 0 0 0 1 0 80 2 0 0 GMT 0
#> 10 1981-07-01 0 0 0 1 6 81 3 181 0 GMT 0
#> 11 1982-07-01 0 0 0 1 6 82 4 181 0 GMT 0
#> 12 1983-07-01 0 0 0 1 6 83 5 181 0 GMT 0
#> 13 1985-07-01 0 0 0 1 6 85 1 181 0 GMT 0
#> 14 1988-01-01 0 0 0 1 0 88 5 0 0 GMT 0
#> 15 1990-01-01 0 0 0 1 0 90 1 0 0 GMT 0
#> 16 1991-01-01 0 0 0 1 0 91 2 0 0 GMT 0
#> 17 1992-07-01 0 0 0 1 6 92 3 182 0 GMT 0
#> 18 1993-07-01 0 0 0 1 6 93 4 181 0 GMT 0
#> 19 1994-07-01 0 0 0 1 6 94 5 181 0 GMT 0
#> 20 1996-01-01 0 0 0 1 0 96 1 0 0 GMT 0
#> 21 1997-07-01 0 0 0 1 6 97 2 181 0 GMT 0
#> 22 1999-01-01 0 0 0 1 0 99 5 0 0 GMT 0
#> 23 2006-01-01 0 0 0 1 0 106 0 0 0 GMT 0
#> 24 2009-01-01 0 0 0 1 0 109 4 0 0 GMT 0
#> 25 2012-07-01 0 0 0 1 6 112 0 182 0 GMT 0
#> 26 2015-07-01 0 0 0 1 6 115 3 181 0 GMT 0
#> 27 2017-01-01 0 0 0 1 0 117 0 0 0 GMT 0
dt2df(Sys.Date() + 0:9) # date
#> Sys.Date() + 0:9 sec min hour mday mon year wday yday isdst zone gmtoff
#> 1 2025-02-06 0 0 0 6 1 125 4 36 0 UTC 0
#> 2 2025-02-07 0 0 0 7 1 125 5 37 0 UTC 0
#> 3 2025-02-08 0 0 0 8 1 125 6 38 0 UTC 0
#> 4 2025-02-09 0 0 0 9 1 125 0 39 0 UTC 0
#> 5 2025-02-10 0 0 0 10 1 125 1 40 0 UTC 0
#> 6 2025-02-11 0 0 0 11 1 125 2 41 0 UTC 0
#> 7 2025-02-12 0 0 0 12 1 125 3 42 0 UTC 0
#> 8 2025-02-13 0 0 0 13 1 125 4 43 0 UTC 0
#> 9 2025-02-14 0 0 0 14 1 125 5 44 0 UTC 0
#> 10 2025-02-15 0 0 0 15 1 125 6 45 0 UTC 0
##' Even simpler: Date -> Matrix - dropping time info {sec,min,hour, isdst}
d2mat <- function(x) simplify2array(unclass(as.POSIXlt(x))[4:7])
## e.g.,
d2mat(seq(as.Date("2000-02-02"), by=1, length.out=30)) # has R 1.0.0's release date
#> mday mon year wday
#> [1,] 2 1 100 3
#> [2,] 3 1 100 4
#> [3,] 4 1 100 5
#> [4,] 5 1 100 6
#> [5,] 6 1 100 0
#> [6,] 7 1 100 1
#> [7,] 8 1 100 2
#> [8,] 9 1 100 3
#> [9,] 10 1 100 4
#> [10,] 11 1 100 5
#> [11,] 12 1 100 6
#> [12,] 13 1 100 0
#> [13,] 14 1 100 1
#> [14,] 15 1 100 2
#> [15,] 16 1 100 3
#> [16,] 17 1 100 4
#> [17,] 18 1 100 5
#> [18,] 19 1 100 6
#> [19,] 20 1 100 0
#> [20,] 21 1 100 1
#> [21,] 22 1 100 2
#> [22,] 23 1 100 3
#> [23,] 24 1 100 4
#> [24,] 25 1 100 5
#> [25,] 26 1 100 6
#> [26,] 27 1 100 0
#> [27,] 28 1 100 1
#> [28,] 29 1 100 2
#> [29,] 1 2 100 3
#> [30,] 2 2 100 4
# \donttest{
## Julian Day Number (JDN, https://en.wikipedia.org/wiki/Julian_day)
## is the number of days since noon UTC on the first day of 4317 BCE.
## in the proleptic Julian calendar. To more recently, in
## 'Terrestrial Time' which differs from UTC by a few seconds
## See https://en.wikipedia.org/wiki/Terrestrial_Time
julian(Sys.Date(), -2440588) # from a day
#> [1] 2460713
#> attr(,"origin")
#> [1] -2440588
floor(as.numeric(julian(Sys.time())) + 2440587.5) # from a date-time
#> [1] 2460713
# }