Re: [R] Serial Date

From: Allan Engelhardt <allane_at_cybaea.com>
Date: Mon, 14 Mar 2011 10:36:20 +0000

On 14/03/11 02:00, Raoni Rosa Rodrigues wrote:
> Hello R Help,
>
> I'm working in a project with a software that register date and time data in serial time format. This format is used by excel, for exemple. In this format, 40597.3911423958 is 2011/2/23 09:23:15.

Not on my system, but this should get you going:

( a<- as.POSIXct("2011-02-23 09:23:15.00001", tz="GMT") ) # [1] "2011-02-23 09:23:15 GMT"
( b<- difftime(a, ISOdatetime(1900,1,1,0,0,0), tz="GMT", units="days") ) # Time difference of 40595.39 days
as.double(b)
# [1] 40595.39
options("digits.secs" = 6)
ISOdatetime(1900, 1, 1, 0, 0, 0) + 40597.3911423958*60*60*24 # TZ dependent
> [1] "2011-02-25 09:23:14.702997 GMT"
Hope this helps a little.

Allan

> First part is number os days since 1900/1/1, and second part is a fraction of a day.
>
> I need to make this transformation in R, and use it to make some algebrian operations. I found that function 'serialNumber' of package 'cxxPack' transform a as.data class object in this format, but without time fraction. But I can't find nothing to do the inverse way, transform serial date format in a POSIX class, for exemple.
>
> Since now, thanks for your time and atention.
>
> All best,
>
> Raoni
> Associate Researcher
> Fish Passage Center
> UFMG, Brazil.
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