[R] How to convert number (matlab) to date

[Prof Brian Ripley]

> but even this is dubious, since there is no year 0 AD. In Gregorian
> and Julian calendars, 1 BC continues directly into 1 AD.

True, but these days we are ruled by ISO 8601:2004, which does define 
a year 0 (the year before 1CE aka 1AD). See
http://en.wikipedia.org/wiki/0_(year) .

It seems also to redefine the meaning of 'Gregorian calendar' calling 
what you are referring to the 'BC/AD calendar system'.  (Those who 
prefer BCE/CE to BC/AD might note the usage of the latter in the 
definitive international standard.)


On Mon, 18 Jul 2011, peter dalgaard wrote:

>
> On Jul 18, 2011, at 14:08 , Gabor Grothendieck wrote:
>
>> On Sat, Jul 16, 2011 at 11:50 PM, Eduardo M. A. M. Mendes
>> <emammendes at gmail.com> wrote:
>>> Hello
>>>
>>> I am new to R and I need to convert some dates (numeric format by matlab) to actual dates in R.
>>>
>>> For instance,
>>>
>>> Matlab -> 730456 -> >> datestr(730456)
>>>
>>> ans =
>>>
>>> 02-Dec-1999
>>>
>>
>> Set the origin to Matlab's origin like this.  Be sure you are using
>> the indicated version of zoo or later:
>>
>>> library(zoo)
>>> packageVersion("zoo")
>> [1] ‘1.7.1’
>>> as.Date(730456, origin = "0000-00-00")
>> [1] "1999-12-02"
>
> Doesn't work on a Mac, and in general, I think it depends on a quirk in your OS's date conversion utilities. What does work for me is
>
>> as.Date(730456-1, origin='0000-01-01')
> [1] "1999-12-02"
>
> but even this is dubious, since there is no year 0 AD. In Gregorian 
> and Julian calendars, 1 BC continues directly into 1 AD.
>
> So, to be sure, try
>
>> as.Date(730456-367, origin='0001-01-01')
> [1] "1999-12-02"
>
> (from which it transpires that the non-existing year 0 is a leap year...).
>
> Or, or course, just use the appropriate "magic constant" of 719529 and begone with it:
>
>> as.Date(730456-719529)
> [1] "1999-12-02"
>
>
> I fail to see what "zoo" has to do with this at all!
>
>
> -- 
> Peter Dalgaard
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
>
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>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595