[R] Re: Julian dates

[Stefano Calza]

origin is a different matter than cut.off. That happens as in chron there's a call to convert.dates and here to expand.year. If you look into the code you see that this function 
convert 2 digits years (e.g. 30 to 1930). The cut of is set to 30. So 27 -> 20027, 31 -> 1931. origin is just needed as dates actually are numbers (seconds if I remenber right) from 
some fixed day, default to 01/01/1970.

 
HIH,
Stefano

> 
> On Wed, Jan 28, 2004 at 04:38:37PM -0000, Ted Harding wrote:
> > On 28-Jan-04 Massimiliano Tripoli wrote:
> > > Hi all,
> > > I have problems with years of dates using "chron" package.
> > > I don't understand why R by this istruction:
> > >> dates("01/02/29",out.format="d/m/year")
> > > [1] 02/Jan/2029
> > > 
> > >> dates("01/02/30",out.format="d/m/year")
> > > [1] 02/Jan/1930
> > > 
> > > reads "29" as 2029
> > > and "30" as 1930. How could I change to read "00" to "05" like 2000 to
> > > 2005 and "06" to "99" like 1906 to 1999 ?
> > 
> > I'm puzzled by the above:
> > 
> > > dates("01/02/29",out.format="d/m/year")
> > [1] 02/Jan/2029
> > > dates("01/02/30",out.format="d/m/year")
> > [1] 02/Jan/1930
> > 
> > so chron apparently acts as though time began at 01/01/1930.
> > 
> > However:
> > 
> > > ?chron
> > -->
> >  origin.: a vector specifying the date with respect to which Julian
> >           dates are computed.  Default is 'c(month = 1, day = 1,
> >           year = 1970)'
> > 
> > (which is the orthodox origin of time according to Unix) and, indeed,
> > 
> > > origin(dates("01/02/29",out.format="d/m/year"))
> > month   day  year 
> >     1     1  1970 
> > 
> > So why does Massimiliano's example behave as though the origin
> > were 01/01/1930?
> > 
> > Best wishes,
> > Ted.
> > 
> > 
> > --------------------------------------------------------------------
> > E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
> > Fax-to-email: +44 (0)870 167 1972
> > Date: 28-Jan-04                                       Time: 16:38:37
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