[R] DateTime Math in R - POSIXct

[Bill.Venables at csiro.au]

Perhaps because the timezone is specified as a character string and not a date-time object complete with timezone.

>From the help filr for as.POSIXct.numeric:

"origin: 	a date-time object, or something which can be coerced by as.POSIXct(tz="GMT") to such an object." 

Note the coercion.

Bill Venables.


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Galen Moore
Sent: Tuesday, 31 May 2011 12:20 PM
To: r-help at r-project.org
Subject: [R] DateTime Math in R - POSIXct

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

> 

> dateP2 <- as.POSIXct(dateN, origin="1970-01-01", tzone="MDT")

> dateP2

[1] "2011-05-22 18:45:00 MDT"

 

Many thanks.

 

Galen Moore


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