[R] as.Date question

[Jason Morgan]

Hello,

On 2009.12.20 18:06:17, MAL wrote:
> All!
> 
> This piece of code:
> 
> zzz1 <- as.POSIXct("1999-03-18", tz="CET")
> zzz2 <- as.POSIXlt("1999-03-18", tz="CET")
> zzz1 == zzz2
> as.Date(zzz1)
> as.Date(zzz2)
> 
> yields TRUE for "zzz1==zzz2", but the two dates returned by as.Date are different:
> 
> > as.Date(zzz1)
> [1] "1999-03-17"
> > as.Date(zzz2)
> [1] "1999-03-18"
> 
> I'm using R 2.10.0.
> 
> Would be glad for any clarifications. Thanks!

I don't know why as.Date() is giving different results, but if look at
the value of the variables, they are equal:

> zzz1 <- as.POSIXct("1999-03-18", tz="CET")
> zzz2 <- as.POSIXlt("1999-03-18", tz="CET")
> zzz1 == zzz2
[1] TRUE
> as.Date(zzz1)
[1] "1999-03-17"
> as.Date(zzz2)
[1] "1999-03-18"
> zzz1
[1] "1999-03-18 CET"
> zzz2
[1] "1999-03-18 CET"

Maybe someone here can explain the behavior of as.Date().

Cheers,
~Jason


-- 
Jason W. Morgan
Graduate Student
Department of Political Science
*The Ohio State University*
154 North Oval Mall
Columbus, Ohio 43210