[R] POSIXct issue

[Prof Brian Ripley]

On Fri, 7 Jan 2011, Rustamali Manesiya wrote:

> Hello I have trouble getting my original datetime back see below. I hope I
> am missing something. Please help.

The numeric form (which you should never use) has an origin at 
midnight in UTC, not EST.

Note too that 'EST' is not very plausible for your timezone (or are 
you in Canada?): see ?Sys.timezone.

> tt <- as.POSIXct(ttn,origin='1970-01-01',tz="UTC")
> attr(tt, "tzone") <- "EST"
> tt
[1] "2011-01-07 07:49:13 EST"


>> tt <- as.POSIXct("2011-01-07 07:49:13", tz="EST")
>> tt
> [1] "2011-01-07 07:49:13 EST"
>> ttn <- as.numeric(tt)
>> ttn
> [1] 1294404553
>> tt <- as.POSIXct(ttn,origin='1970-01-01',tz="EST")
>> tt
> [1] "2011-01-07 12:49:13 EST"
>>
>
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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)
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