[R] strptime and "impossible" dates

[Prof Brian Ripley]

On Tue, 24 Jul 2001, David Kane  <David Kane wrote:

> Typically, when I use strptime with "impossible" dates I get an NA, which is
> what I expect.
>
> > version
>          _
> platform sparc-sun-solaris2.6
> arch     sparc
> os       solaris2.6
> system   sparc, solaris2.6
> status
> major    1
> minor    3.0
> year     2001
> month    06
> day      22
> language R
> > strptime("20001132", format = "%Y%m%d")
> [1] "NA"
>
> But this is not always the case, consider the impossible case of November 31, 2000
>
> > strptime("20001131", format = "%Y%m%d")
> [1] "2000-12-01"
>
> Shouldn't the answer here be NA? I would submit this as a bug except that I
> suspect that the problem is my misunderstanding of the role of seconds and time
> zones is this function . . .

> Thanks for any pointers. I have read the help pages and the excellent
> discussion in the recent R Newsletter.

It depends on the system's strptime.  But it would be usual for
out-of-range dates to get normalized as you saw.  In general `invalid'
local times (POSIXlt structures) are fixed if they are not seriously
adrift.


-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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