weekdays  R Documentation 
Extract the weekday, month or quarter, or the Julian time (days since some origin). These are generic functions: the methods for the internal datetime classes are documented here.
weekdays(x, abbreviate) ## S3 method for class 'POSIXt' weekdays(x, abbreviate = FALSE) ## S3 method for class 'Date' weekdays(x, abbreviate = FALSE) months(x, abbreviate) ## S3 method for class 'POSIXt' months(x, abbreviate = FALSE) ## S3 method for class 'Date' months(x, abbreviate = FALSE) quarters(x, abbreviate) ## S3 method for class 'POSIXt' quarters(x, ...) ## S3 method for class 'Date' quarters(x, ...) julian(x, ...) ## S3 method for class 'POSIXt' julian(x, origin = as.POSIXct("19700101", tz = "GMT"), ...) ## S3 method for class 'Date' julian(x, origin = as.Date("19700101"), ...)
x 
an object inheriting from class 
abbreviate 
logical vector (possibly recycled). Should the names be abbreviated? 
origin 
an lengthone object inheriting from class

... 
arguments for other methods. 
weekdays
and months
return a character
vector of names in the locale in use.
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 leapseconds.
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
.
DateTimeClasses
, Date
weekdays(.leap.seconds) months(.leap.seconds) quarters(.leap.seconds) ## 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)), stringsAsFactors = FALSE) { DF < as.data.frame(unclass(as.POSIXlt( dt )), stringsAsFactors=stringsAsFactors) `names<`(cbind(dt, DF, deparse.level=0L), c(dName, names(DF))) } ## e.g., dt2df(.leap.seconds) # date+time dt2df(Sys.Date() + 0:9) # date ##' 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("20000202"), by=1, length.out=30)) # has R 1.0.0's release date ## 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 BC. ## 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 floor(as.numeric(julian(Sys.time())) + 2440587.5) # from a datetime
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