[R] ISOdate() and strptime()

[Prof Brian Ripley]

On Fri, 14 Nov 2003, RINNER Heinrich wrote:

> Dear R-people!
> 
> I am using R 1.8.0, under Windows XP.
> While using ISOdate() and strptime(), I noticed the following behaviour when
> "wrong" arguments (e.g., months>12) are given to these functions:
> 
> > ISOdate(year=2003,month=2,day=20) #ok
> [1] "2003-02-20 13:00:00 Westeuropäische Normalzeit"
> > ISOdate(year=2003,month=2,day=30) #wrong day, but returns a value
> [1] "2003-03-02 13:00:00 Westeuropäische Normalzeit"
> > ISOdate(year=2003,month=2,day=35) #wrong day, and returns NA
> [1] NA
> > ISOdate(year=2003,month=2,day=40) #wrong day, but returns a value
> [1] "2003-02-04 01:12:00 Westeuropäische Normalzeit"
> > ISOdate(year=2003,month=22,day=20) #wrong month, but returns a value
> [1] "2003-02-02 21:12:00 Westeuropäische Normalzeit"
> 
> And almost the same with strptime():
> > strptime("2003-02-20", format="%Y-%m-%d")
> [1] "2003-02-20"
> > strptime("2003-02-30", format="%Y-%m-%d")
> [1] "2003-03-02"
> > strptime("2003-02-35", format="%Y-%m-%d")
> [1] NA
> > strptime("2003-02-40", format="%Y-%m-%d")
> [1] "2003-02-04"
> > strptime("2003-22-20", format="%Y-%m-%d")
> [1] NA
> 
> Is this considered to be a user error ("If you put garbage in, expect to get
> garbage out"), or would it be safer to generally return Nas, as in
> ISOdate(year=2003,month=2,day=35)?

Expect to get the best guess at what you intended, and expect this to 
depend on your OS.

-- 
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