[R] as.POSIXct problem

[Gabor Grothendieck]

I was unable to reproduce your error on Windows 2000 R 1.8.1:

> testDATES<-c(35947,35971,36004,36008,36053,36066)
> 
> testDATES<-chron(dates=testDATES, format = c(dates = "m/d/y"), 
+ origin=c(month = 12, day = 30, year = 1899))
> 
> as.POSIXct(testDATES)
[1] "1998-05-31 20:00:00 Eastern Daylight Time"
[2] "1998-06-24 20:00:00 Eastern Daylight Time"
[3] "1998-07-27 20:00:00 Eastern Daylight Time"
[4] "1998-07-31 20:00:00 Eastern Daylight Time"
[5] "1998-09-14 20:00:00 Eastern Daylight Time"
[6] "1998-09-27 20:00:00 Eastern Daylight Time"
> 

At any rate, one idea is to create the chron dates 
relative to the default origin like this:

> testDATES<-c(35947,35971,36004,36008,36053,36066)
> testDATES.chron <- chron("12/30/1899") + testDATES
> as.POSIXct(testDATES.chron)
[1] "1998-05-31 20:00:00 Eastern Daylight Time"
[2] "1998-06-24 20:00:00 Eastern Daylight Time"
[3] "1998-07-27 20:00:00 Eastern Daylight Time"
[4] "1998-07-31 20:00:00 Eastern Daylight Time"
[5] "1998-09-14 20:00:00 Eastern Daylight Time"
[6] "1998-09-27 20:00:00 Eastern Daylight Time"

Does that make any difference on your system?

---
Date:   Fri, 5 Mar 2004 11:35:45 -0500 
From:   Brian Beckage <Brian.Beckage at uvm.edu>
To:   <r-help at stat.math.ethz.ch> 
Subject:   [R] as.POSIXct problem 

 
Hi all,

I'm having difficulty converting a 'dates' object to a POSIXct object:

testDATES<-c(35947,35971,36004,36008,36053,36066)

testDATES<-chron(dates=testDATES, format = c(dates = "m/d/y"), 
origin=c(month = 12, day = 30, year = 1899))

>[1] 06/01/98 06/25/98 07/28/98 08/01/98 09/15/98 09/28/98

> as.POSIXct(testDATES)
[1] NA NA NA NA NA NA

>format(as.POSIXct(testDATES), "%m/%d/%Y")
[1] NA NA NA NA NA NA

I've looked at the as.POSIXct function, traced the problem to ISOdate 
and then to strptime, e.g.,

x<-paste(year=1899, month=12, day=30, hour=12, min=0, sec=0)
>x
>"1899 12 30 12 0 0"

strptime(x, "%Y %m %d %H %M %S")
[1] NA NA NA NA

However, strptime works fine below.

dates <- c("02/27/92", "02/27/92", "01/14/92",
"02/28/92", "02/01/92")
strptime(dates, "%m/%d/%y")
>"02/27/92" "02/27/92" "01/14/92" "02/28/92" "02/01/92"

I've been reading through a whole suite of emails on the R archives 
regarding as.POSIXct problems but I have not found anything that 
solves my particular problem. I need the dates to be of class 
POSIXct for use in the its package.

I'm using R 1.8.1 on Mac OS 10.3.2. Any help is greatly appreciated.

Thanks,
Brian


-- 
*********************************************************************
Brian Beckage
Department of Botany
University of Vermont
Marsh Life Science Building
Burlington, VT 05405