1\name{day.of.week}
2\alias{day.of.week}
3\alias{julian.default}
4\alias{leap.year}
5\alias{month.day.year}
6\title{
7  Convert between Julian and Calendar Dates
8}
9\description{
10  Utility functions to convert between Julian dates (numbers of days
11  since an origin, by default 1970-01-01) and calendar dates given by
12  year, month, and day within the month.
13}
14\usage{
15\method{julian}{default}(x, d, y, origin., \dots)
16month.day.year(jul, origin.)
17leap.year(y)
18day.of.week(month, day, year)
19}
20\arguments{
21  \item{x, month}{vector of month numbers.}
22  \item{d, day}{vector of day numbers.}
23  \item{y, year}{vector of years.}
24  \item{jul}{vector of Julian Dates, i.e., number of days since
25    \code{origin.}.}
26  \item{origin.}{vector specifying the origin as month, day, and year.
27    If missing, it defaults to \code{getOption("chron.origin")} if this
28    is non-null, otherwise
29    \code{c(month = 1, day = 1, year = 1970)}.}
30  \item{\dots}{further arguments to be passed to or from methods.}
31}
32\value{
33  A vector of Julian dates (number of days since \code{origin.}) when
34  \code{julian()} is called, or a list with members \code{month},
35  \code{day}, \code{year} corresponding to the input Julian dates if
36  \code{month.day.year()} is called.  \code{leap.year()} returns a
37  logical vector indicating whether the corresponding year is a leap
38  year.
39  \code{day.of.week()} returns a number between 0 and 6 to specify day
40  of the week--0 refers to Sunday.
41
42  These functions were taken from Becker, Chambers, and Wilks (1988),
43  and were slightly modified to take \code{chron} and \code{dates}
44  objects; some also take the extra argument \code{origin.}.
45  %The original functions are stored in the \code{library(example)}.
46}
47\seealso{
48  \code{\link{chron}},
49  \code{\link{dates}},
50  \code{\link{times}}
51}
52\examples{
53julian(1, 1, 1970)
54# [1] 0
55unlist(month.day.year(0))
56# month   day  year
57#     1     1  1970
58}
59\keyword{chron}
60