From murdoch at stats.uwo.ca  Wed Sep 17 22:06:48 2008
From: murdoch at stats.uwo.ca (Duncan Murdoch)
Date: Wed, 17 Sep 2008 16:06:48 -0400
Subject: [Rd] Dates in C api
In-Reply-To: <575EAD86322DA342B50FE422364A9F52082D528B@NYWEXMB27.msad.ms.com>
References: <575EAD86322DA342B50FE422364A9F52082D528B@NYWEXMB27.msad.ms.com>
Message-ID: <48D16358.1050606@stats.uwo.ca>

On 9/17/2008 1:24 PM, Lee, Philip (IT) wrote:
> r-devel,
> 
> I've been trying to write a C plugin for R, and I'm struggling to
> understand how dates are represented.
> 
> I can create a date in R:
>> mydate<-as.Date(1, origin="1900-01-01") mydate
> [1] "1900-01-02"

See ?Date for the internal represention: it's a count of days from a 
particular epoch.

> When I pass my date to a plugin, though, it's type is that of a real.
> There doesn't seem to be a date type in Rinternals.h, is there a way to
> recognize that a value is a date rather than a real?

Look at the class attribute.
> 
> Equally, does anyone know if it's possible to create date values in the
> C api?

Create a vector of doubles, and attach the right class to it.  See 
section 5.8.5 of the R extensions manual for an example.

Duncan Murdoch

> 
> Thanks,
> Phil Lee
> 
> Philip Lee
> Morgan Stanley | Technology
> 750 Seventh Avenue, 12th Floor | New York, NY  10019
> Phil.Lee at morganstanley.com
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[Rd] Dates in C api
Duncan Murdoch