I wrote the date package long ago, and it has been useful. In my current task
of reunifying the R (Tom Lumley) and Splus (me) code trees for survival, I'm
removing the explicit dependence on 'date' objects from the expected survival
routines so that they better integrate. Comparison of 'date' to 'Date' has
raised a couple of questions.
Clearly Date is more mature -- more options for conversion, better plotting,
etc (a long list of etc). I see three things where date is better. Only the
last of these really matters, and is the point on which I would like comment.
(Well, actually I'd like to talk you all into a change, of course).
1. Since date uses 1/1/1960 as the base, and so does SAS, those of us who
contantly pass files back and forth between those two packages have a slightly
easier time.
2. as.date(10) works, as.Date(10) does not. Sometimes I have done a
manipluation that the date package does not understand, and I know that the
result is still of the right type, but the package does not. However, this is
fairly rare and I can work around it. (It mostly occurs in processing the rate
tables for expected survival).
3. temp <- as.Date('1990/1/1') - as.date('1953/2/5')
sqrt(temp)
Error in Math.difftime(temp3) : sqrtnot defined for "difftime" objects
Minor bug: no space before the word 'not'
Major: this shouldn't fail.
People will do things with time intervals that you have not thought of.
Fitting
a growth curve that uses a square root, for instance. I firmly believe that
the
superior behavior in the face of something unexpected is to assume that the
user
knows what they are doing, and return a numeric.
I recognize that "assume the user knows what they are doing" is an anathema
to the more zealous OO types, but in designing a class I have found that they
often know more than me!
4. Variation on #3 above
> (as.Date('2007-9-14') - as.Date('1953-3-10')) / 365.25
Time difference of 54.51335 days
No, I am not 54.5 days old. Both hair color and knee creaking most
definitely proclaim otherwise, I am sorry to say. Time difference / number
should be a number.
5. This is only amusing. Im not saying that as.Date should necessarily
work,
but the format is certainly not ambiguous. (Not standard, but not ambiguous).
Not important to fix, not something that date does any better.
> as.Date('09Sep2007')
Error in fromchar(x) : character string is not in a standard unambiguous format
Terry Therneau
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