[R] Serial Date

[Gabor Grothendieck]

On Tue, Mar 15, 2011 at 11:42 PM, Raoni Rosa Rodrigues
<raonirosa at yahoo.com.br> wrote:
> Hello Mr. Grothendieck,
>
> thanks for your reply!
>
> Text book that I use (Spector, 2008) dind't comment about this feature of chron function...
>
> I just don't understand why we have 10957 days of difference between dates (look that date on your mail seems to be 1981, not 2011), and not the 25568 days expected due the difference in origin: 1/1/1900 of excel against 1/1/1970 of chron package.
>

As mentioned in my last post you can adjust for that.  To be explicit,
calculate the difference, d, between origins and adjust all date/times
by that amount:

> # Difference between what you get & what you want
> as.numeric(chron(floor(40597.3911423958)) - chron("2/23/2011"))
[1] 25569
>
> # Difference between origins
> # This should match last calculation.
> d <- as.numeric(chron(0) - chron("12/30/1899"))
[1] 25569
>
> # now that we have d we adjust all dates using it
> chron(40597.3911423958) - d
[1] (02/23/11 09:23:15)

As mentioned in R News 4/1 there is an option to set chron's origin
but its not recommended that you use the chron options and its
preferable to simply adjust all dates as shown.

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