Re: [R] help with POSIX

[Thomas Lumley]

On Fri, 22 Apr 2005, Ghosh, Sandeep wrote:
For the r script below
datestr <- "01/01/2004"
as.POSIXct(as.Date(datestr, "%d/%m/%Y"))
I get the following output
"2003-12-31 18:00:00 Central Standard Time"
Why is the date a day before. I guess its something to do with the time, 
but is there a way to get it to return 2004-01-01 instead?
Yes.
If you want POSIXt, which includes time as well as date and so depends on 
time zone, use it.
datestr <- "01/01/2004"
strptime(datestr, "%d/%m/%Y")
[1] "2004-01-01"
class(strptime(datestr, "%d/%m/%Y"))
[1] "POSIXt"  "POSIXlt"
as.POSIXct(strptime(datestr, "%d/%m/%Y"))
[1] "2004-01-01 Pacific Standard Time"
If you just want a date, just use Date
as.Date(datestr, "%d/%m/%Y")
[1] "2004-01-01"
When you convert from Date to POSIXt it has to pick an arbitrary time 
within the day, and it picks midnight GMT.

        -thomas
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