On May 30, 2011, at 10:20 PM, Galen Moore wrote:
Greetings -
I'm battling POSIXct, as per the code below. My input is actually
an XL
file, but the weird results below correctly model what I am seeing
in my
program.
Before I punt and use lubridate or timeDate, could anyone please
help me
understand why POSIXct forces my variable back to GMT?
I suspect that I'm not properly coding the tzone value, but it does
not
throw an error as-is.
tstamp <- "2011-05-22 11:45:00 MDT"
mode(tstamp)
[1] "character"
dateP <- as.POSIXct(tstamp, origin="1970-01-01", tzone="MDT")
mode(dateP)
[1] "numeric"
dateP
[1] "2011-05-22 11:45:00 MDT"
dateN <- as.numeric(dateP)
dateN
[1] 1306086300
So now the internal representation is referenced to GMT
dateP2 <- as.POSIXct(dateN, origin="1970-01-01", tzone="MDT")
dateP2
And you are telling the function to add as many hours offset as needed
for the difference between GMT and MD T.....
--
David.
[1] "2011-05-22 18:45:00 MDT"
David Winsemius, MD
West Hartford, CT
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