# weekday.POSIXt: Extract Parts of a POSIXt or Date Object

### Description

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

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23``` ```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("1970-01-01", tz = "GMT"), ...) ## S3 method for class 'Date' julian(x, origin = as.Date("1970-01-01"), ...) ```

### Arguments

 `x` an object inheriting from class `"POSIXt"` or `"Date"`. `abbreviate` logical vector (possibly recycled). Should the names be abbreviated? `origin` an length-one object inheriting from class `"POSIXt"` or `"Date"`. `...` arguments for other methods.

### Value

`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 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`.

`DateTimeClasses`, `Date`
 ``` 1 2 3 4 5 6 7 8 9 10 11``` ```weekdays(.leap.seconds) months(.leap.seconds) quarters(.leap.seconds) ## 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 date-time ```