The function jul is used to create jul (julian date)
objects, which are useful for date calculations.
as.jul and asJul coerce an object to class "jul", the
difference being that as.jul calls the constructor jul,
while asJul simply forces the class of its argument to be "jul"
without any checking as to whether or not it makes sense to do so.
is.jul tests whether an object inherits from class "jul".
jul(x, …)
# S3 method for Date
jul(x, …)
# S3 method for IDate
jul(x, …)
# S3 method for ti
jul(x, offset = 1, …)
# S3 method for yearmon
jul(x, offset = 0, …)
# S3 method for yearqtr
jul(x, offset = 0, …)
# S3 method for default
jul(x, …)
as.jul(x, …)
asJul(x)
is.jul(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.
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 x has tif = "wmonday" so
that x represents a week ending on Monday, than any
offset in the range [0, 1/7] will return the Tuesday of that
week, while offset in the range (1/7, 2/7] will return the
Wednesday of that week, offset in the range (6/7, 1] will
return the Monday that ends the week, and so on.
jul.yearmon and jul.yearqtr work on yearmon and
yearqtr objects from zoo. Note that the default
offset for these functions is 0, not 1, as that is how the
other index-to-date functions in zoo work, i.e, if ym
is a yearmon object, then as.Date(ym) and
as.jul(ym) should give the same date.
is.jul returns TRUE or FALSE.
as.jul and asJul return objects with class "jul".
jul constructs a jul object like x.
jul with no arguments returns the jul for the current day.
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.
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. A recent addition is a method to
handle IDate objects as defined in the data.table
package.
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.
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.
# NOT RUN {
dec31 <- jul(20041231)
jan30 <- jul("2005-1-30")
jan30 - dec31 ## 30
feb28 <- jan30 + 29
jul() ## current date
# }
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