On Thu, 22 Jan 2009, Terry Therneau wrote:
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However, as.Date encounters an error when the string does not represent an
actual date.
eg:
> date1 <- "2009-02-29" # Note: 2009 not a leap year
as.Date(date1)
Error in fromchar(x) :
character string is not in a standard unambiguous format
As I have many instances of date entries like this, date1, date2, date3,
etc. , I'd like the script to error out gracefully and to be able to point
the user to which date they need to correct, rather than "Error in
fromchar(x)...", which doesn't make it obvious what they need to do to fix
the error.
Ideally I'd love to send the user a message like:
print(paste(date1, "is an invalid date. Refer to calendar.", sep=" "))
If anyone has any suggestions on catching this type of error and feedback
which directs the user, it would be much appreciated.
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One idea is to use the as.date function, for the older (and less capable) 'date'
class. This is currently loaded by default with library(survival). It returns
NA for an invalid date rather than dying.
So does as.Date *if you specify the format* (as you have to with your
as.date: it has a default one):
as.Date(date1, format="%Y-%m-%d")
[1] NA
as.date(c("2009-5-10", "2007/2/29", "1953/3/10"), order='ymd')
[1] 10May2009 NA 10Mar53
The order argument in needed here since the default assumption is the US habit
of month-day-year.
You can then convert to the more modern format.
temp <- as.date(c("2009-5-10", "2007/2/29", "1953/3/10"), order='ymd')
as.Date(temp)
[1] "2009-05-10" NA "1953-03-10"
Terry Therneau
Note: as.Date will return a string with NA's as well, AS LONG AS the first date
in the sequence is legal. It uses the first to pick a format (I presume).
--
Brian D. Ripley, rip...@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
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