[R] problem with unlist POSIX date at midnight

[Prof Brian Ripley]

On Wed, 17 Jan 2007, Hanneke Schuurmans wrote:

> 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....
>
> 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[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
> unlist(strptime(acc.period[17],format="%Y-%m-%d %H:%M:%S"))
> #  sec   min  hour  mday   mon  year  wday  yday isdst
> #   0     0     1     1     2   106     3    59     0
>
> 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
>
> Could someone help?

Please see the footer comment

> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

We do need that to help you.  Using unclass() rather than unlist() will 
help us see what strptime actually returned (I suspect the NAs are from 
there as your (unshown) input was invalid, e.g. had hour=24).

We also need the other information the posting guide asks for, such as the 
output of sessionInfo().

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595