\HeaderA{weekdays}{Extract Parts of a POSIXt or Date Object}{weekdays}
\aliasA{julian}{weekdays}{julian}
\methaliasA{julian.Date}{weekdays}{julian.Date}
\methaliasA{julian.POSIXt}{weekdays}{julian.POSIXt}
\aliasA{months}{weekdays}{months}
\methaliasA{months.Date}{weekdays}{months.Date}
\methaliasA{months.POSIXt}{weekdays}{months.POSIXt}
\aliasA{quarters}{weekdays}{quarters}
\methaliasA{quarters.Date}{weekdays}{quarters.Date}
\methaliasA{quarters.POSIXt}{weekdays}{quarters.POSIXt}
\methaliasA{weekdays.Date}{weekdays}{weekdays.Date}
\methaliasA{weekdays.POSIXt}{weekdays}{weekdays.POSIXt}
\keyword{chron}{weekdays}
\begin{Description}\relax
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.
\end{Description}
\begin{Usage}
\begin{verbatim}
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"), ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] an object inheriting from class \code{"POSIXt"} or \code{"Date"}.
\item[\code{abbreviate}] logical.  Should the names be abbreviated?
\item[\code{origin}] an length-one object inheriting from class
\code{"POSIXt"} or \code{"Date"}.
\item[\code{...}] arguments for other methods.
\end{ldescription}
\end{Arguments}
\begin{Value}
\code{weekdays} and \code{months} return a character
vector of names in the locale in use.

\code{quarters} returns a character vector of \code{"Q1"} to
\code{"Q4"}.

\code{julian} returns the number of days (possibly fractional)
since the origin, with the origin as a \code{"origin"} attribute.
\end{Value}
\begin{Note}\relax
Other components such as the day of the month or the year are
very easy to compute: just use \code{\LinkA{as.POSIXlt}{as.POSIXlt}} and extract
the relevant component.
\end{Note}
\begin{SeeAlso}\relax
\code{\LinkA{DateTimeClasses}{DateTimeClasses}}, \code{\LinkA{Date}{Date}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
weekdays(.leap.seconds)
months(.leap.seconds)
quarters(.leap.seconds)

## Julian Day Number (JDN, http://en.wikipedia.org/wiki/Julian_day)
## is the number of days since noon UTC on the first day of 4317 BC.
julian(Sys.Date(), -2440588) # for a day
floor(as.numeric(julian(Sys.time())) + 2440587.5) # for a date-time
\end{ExampleCode}
\end{Examples}

