AW: [R] ISOdate() and strptime()
Thanks for this clarification. I have learned in the meantime that it is necessary to be very careful when using all these POSIX things. As another example, here is something that made me scratch my head just yesterday: When I create a sequence of days that happens to start before and ends in daylight savings time, I seem to lose a day: seq(from = strptime(20030329, format=%Y%m%d), to= strptime(20030402, format=%Y%m%d), by=DSTday) [1] 2003-03-29 Westeuropäische Normalzeit 2003-03-30 Westeuropäische Normalzeit [3] 2003-03-31 Westeuropäische Sommerzeit 2003-04-01 Westeuropäische Sommerzeit seq(from = strptime(20030329, format=%Y%m%d), to= strptime(20030402, format=%Y%m%d), by=day) [1] 2003-03-29 00:00:00 Westeuropäische Normalzeit 2003-03-30 00:00:00 Westeuropäische Normalzeit [3] 2003-03-31 01:00:00 Westeuropäische Sommerzeit 2003-04-01 01:00:00 Westeuropäische Sommerzeit Again, my expectations might be wrong here, and there will be good reasons why I get this result (my OS again?). But considering all these subtle issues I have encountered so far, personally I can understand why some people suggested that it may be easier to use the chron or date package (especially if you are a beginner, have no prior experience with all these things, and don't want to worry about time zones, DST, or the pitfalls of your OS). At least it was useful for me to cross-check the results I obtained with POSIX with the results using chron. The POSIX classes are a great thing, but as they are much more powerful, they are also more complex and have more things to watch out for and more traps to fall in (for me at least ;-)). -Heinrich. -Ursprüngliche Nachricht- Von: Prof Brian Ripley [mailto:[EMAIL PROTECTED] Gesendet: Samstag, 22. November 2003 20:56 An: RINNER Heinrich Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Betreff: Re: [R] ISOdate() and strptime() Confirmation that this *is* an OS-specific problem: A professional implementation of the POSIX standard (Solaris) gets all of these correct. Your so-called OS lacks any implementation of strptime, so we borrowed one from glibc. Unfortunately, that is buggy, even to the extent that unclass(strptime(2003-22-20, format=%Y-%m-%d)) unclass(strptime(2003 22 20, format=%Y %m %d)) give different answers! (And RH8.0 gives the same answers as the substitute code used on R for Windows.) I believe Simon Fear owes the R-developers a public apology for his (not properly referenced in the archives) reply to this thread. BDR On Fri, 14 Nov 2003, Prof Brian Ripley wrote: 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., months12) 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, [EMAIL PROTECTED] 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, UKFax: +44 1865 272595 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] ISOdate() and strptime()
Confirmation that this *is* an OS-specific problem: A professional implementation of the POSIX standard (Solaris) gets all of these correct. Your so-called OS lacks any implementation of strptime, so we borrowed one from glibc. Unfortunately, that is buggy, even to the extent that unclass(strptime(2003-22-20, format=%Y-%m-%d)) unclass(strptime(2003 22 20, format=%Y %m %d)) give different answers! (And RH8.0 gives the same answers as the substitute code used on R for Windows.) I believe Simon Fear owes the R-developers a public apology for his (not properly referenced in the archives) reply to this thread. BDR On Fri, 14 Nov 2003, Prof Brian Ripley wrote: 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., months12) 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, [EMAIL PROTECTED] 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, UKFax: +44 1865 272595 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
RE: [R] ISOdate() and strptime()
I think I do understand how difficult dates are. All I'm saying is
that by adopting a standard that is OS dependent (and hence,
almost by definition, OS varying) you make R behave differently
on different OSs - and that is NOT making R portable across
multiple OSs.
This is a theoretical whinge. I'm not going to program it !
Please don't let me make too much of this anyway. For one thing,
although it is not guaranteed, it seems that many OSs DO in
fact behave identically. Also, it is only incomplete or erroneous
dates that might be handled differently - and in most applications,
one needs to pre-process incomplete date-times in R, rather than
leave them to any default interpretation (even if that default was
strictly fixed).
-Original Message-
From: Jason Turner [mailto:[EMAIL PROTECTED]
Sent: 15 November 2003 06:17
To: Simon Fear
Cc: [EMAIL PROTECTED]
Subject: Re: [R] ISOdate() and strptime()
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Thomas Lumley wrote:
On Fri, 14 Nov 2003, Simon Fear wrote:
Is the behaviour of ISOtime() and strptime() determined by ISO
or POSIX standard? Seems not to fit R's no nannying policy
at all.
It's determined by your operating system, so you're
complaining to the
wrong people.
And since R is written to be portable across multiple OSs,
you might get
an idea how tricky this becomes. Hence the iron fist
approach to date
handling. Believe me, I've programmed date handling - it's always a
terrible, nasty, messy business when international locales
and different
operating systems clash. I'm stunned it's as good as it is, subtle
traps and all.
Cheers
Jason
Simon Fear
Senior Statistician
Syne qua non Ltd
Tel: +44 (0) 1379 69
Fax: +44 (0) 1379 65
email: [EMAIL PROTECTED]
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Re: [R] ISOdate() and strptime()
I have followed with interest the discussion on date handling. I am no expert in these things; all I want to do is convert a character vector that has been read into R (and which may contain some erroneous dates) to a date format, and then do some work with it [e.g., use it in a plot]. Classes POSIXlt and POSIXct seem fine to me - for example, they have very nice and useful seq and plot methods. So now I have two more questions: 1. Is it only incomplete or erroneous dates that might be handled differently by ISOdate() or strptime()? Do correct specifications of year, month and day always give the same results, no matter where or who I am? 2. Can someone point me to a reference that helps me understand why R's (or the Operating systems?) best guess at what I intended turns out to be the results in the examples I posted in my earlier mail? Regards, Heinrich. -Ursprüngliche Nachricht- Von: RINNER Heinrich [mailto:[EMAIL PROTECTED] Gesendet: Freitag, 14. November 2003 11:13 An: '[EMAIL PROTECTED]' Betreff: [R] ISOdate() and strptime() 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., months12) 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)? -Heinrich. __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
[R] ISOdate() and strptime()
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., months12) 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)? -Heinrich. __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] ISOdate() and strptime()
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., months12) 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, [EMAIL PROTECTED] 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, UKFax: +44 1865 272595 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
RE: [R] ISOdate() and strptime()
People who don't like this behaviour (and particularly those
who dislike it as much as I do), should consider as.date() from
the dates package as an alternative. Gives you a NA if the
specified date is impossible (at least in all the examples given
earlier).
Is the behaviour of ISOtime() and strptime() determined by ISO
or POSIX standard? Seems not to fit R's no nannying policy
at all. Or maybe it's the future: in version 1.9 will I be able to
type glm() and have R take a best guess at the model
specification I had in mind?
-Original Message-
From: Prof Brian Ripley [mailto:[EMAIL PROTECTED]
Expect to get the best guess at what you intended, and expect this to
depend on your OS.
--
Brian D. Ripley, [EMAIL PROTECTED]
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, UKFax: +44 1865 272595
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Simon Fear
Senior Statistician
Syne qua non Ltd
Tel: +44 (0) 1379 69
Fax: +44 (0) 1379 65
email: [EMAIL PROTECTED]
web: http://www.synequanon.com
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