[R] problem with unlist POSIX date at midnight

[Hanneke Schuurmans]

Dear R-users,

I use unlist of POSIX dates to extract the year, hour etc. With that I 
can search for files in my database which are in the form 
'yyyymmddhh_synops.txt'
However, I get stucked during midnight where unlist just gives NA's.
The script is given below; the problem accurs at acc.period[16] 
(midnight). However when I write out the character, unlist works well. 
But as.character(acc.period[16]) is not the solution....

 > dates=seq(as.Date("2006-03-01"), as.Date("2006-11-01"), "days")
 > i=1
 > begin=paste(dates[i]-1,"09:00:00")
 > end=paste(dates[i],"08:00:00")
 > acc.period=seq(as.POSIXct(begin),as.POSIXct(end),"hour")
 >
 > unlist(strptime(acc.period[15],format="%Y-%m-%d %H:%M:%S"))
  sec   min  hour  mday   mon  year  wday  yday isdst
    0     0    23    28     1   106     2    58     0
 > unlist(strptime(acc.period[16],format="%Y-%m-%d %H:%M:%S"))
  sec   min  hour  mday   mon  year  wday  yday isdst
   NA    NA    NA    NA    NA    NA    NA    NA    -1
 > unclass(strptime(acc.period[16],format="%Y-%m-%d %H:%M:%S"))
$sec
[1] NA

$min
[1] NA

$hour
[1] NA

$mday
[1] NA

$mon
[1] NA

$year
[1] NA

$wday
[1] NA

$yday
[1] NA

$isdst
[1] -1

 >
 > a="2006-03-01 00:00:00"
 > unlist(strptime(a,format="%Y-%m-%d %H:%M:%S"))
  sec   min  hour  mday   mon  year  wday  yday isdst
    0     0     0     1     2   106     3    59     0
 >
 > sessionInfo()
R version 2.4.0 (2006-10-03)
i386-pc-mingw32

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United 
States.1252;LC_MONETARY=English_United 
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] "methods"   "stats"     "graphics"  "grDevices" "utils"     "datasets"
[7] "base"    

Thanks in advance!

Hanneke

-- 
---------------------------------------------
ir J.M. (Hanneke) Schuurmans
PhD student Hydrology
Department of Physical Geography
Faculty of Geosciences - Universiteit Utrecht
P.O. Box 80115  3508 TC  Utrecht
T +31 (0)30 2532988  F +31 (0)30 2531145
W www.geo.uu.nl/staff/schuurmans