fame (version 1.13)

jul: Julian Date Objects

Description

The function jul is used to create jul (julian date) objects, which are useful for date calculations.

as.jul and is.jul coerce an object to a julian date and test whether an object is a jul.

Usage

jul(x, ...)
## S3 method for class 'Date':
jul(x, ...)
## S3 method for class 'ti':
jul(x, offset = 1, ...)
## S3 method for class 'default':
jul(x, ...)
as.jul(x)
is.jul(x)

Arguments

x

object to be tested (is.jul) or converted into a jul object. As described in the details below, the constructor function jul can deal with several different kinds of x.

...

other args to be passed to the method called by the generic function. jul.default may pass these args to as.Date.

offset

for jul.ti, a number in the range [0,1] telling where in the period represented by x to find the day. 0 returns the first day of the period, while the default value 1 returns the last day of the period. For example, if

Value

• is.jul returns TRUE or FALSE. as.jul coerces its argument to have class jul, without making any attempt to discern whether or not this is a sensible thing to do. jul constructs a jul object like x. jul with no arguments returns the jul for the current day.

Details

The jul's for any pair of valid dates differ by the number of days between them. R's Date class defines a Date as a number of days elapsed since January 1, 1970, but jul uses the encoding from the Numerical Recipes book, which has Jan 1, 1970 = 2440588, and the code for converting between ymd and jul representations is a straightforward port of the code from that tome. This also matches the MRA Splus and csh (shell script) julian date routines.

Adding an integer to, or subtracting an integer from a jul results in another jul, and one jul can be subtracted from another. Two jul's can also be compared with the operators (==, !=, <.>, <=,>=).

The jul class implements methods for a number of generic functions, including "[", as.Date, as.POSIXct, as.POSIXlt, c, format, max, min, print, rep, seq, ti, time, ymd. jul is a generic function with specialized methods to handle Date and ti objects. The default method (jul.default) deals with character x by calling as.Date on it. Otherwise, it proceeds as follows:

If x is numeric, isYmd is used to see if it could be yyyymmdd date, then isTime is called to see if x could be a decimal time (a number between 1799 and 2200). If all else fails, as.Date(x) is called to attempt to create a Date object that can then be used to construct a jul.

References

Press, W. H., Teukolsky, S. A., Vetterling, W. T., and Flannery, B. P. (1992). Numerical Recipes: The Art of Scientific Computing (Second Edition). Cambridge University Press.

See Also

jul, ymd, ti, as.Date

Examples

dec31 <- jul(20041231)
jan30 <- jul("2005-1-30")
jan30 - dec31              ## 30
feb28 <- jan30 + 29
jul()                      ## current date