The date library was written 20 or so years ago. It was a very good
first effort, but the newer Date library has superior functionality in
nearly every way. The date library is still available, for legacy
projects such as yours, but I do not advise it for new work. To answer
your specific questions:
1. What you have is a real bug. The underlying C routine that scans
through the text returns "0" as a marker for any string it can't figure
out, a year of 'abc' or month 'charlie' for example. The S function
then turns these into NA. I never, ever thought about year 0. In our
longer term studies at Mayo we have birth dates in the 1800s, it is
rather surprising that a birth date of 1900 hadn't caught me sometime in
the past. I'll fix this.
2. The date library predates the strptime function by over 10 years. It
is not a huge surprise that I neglected to include support for it -- my
oracular abilities are limited. For an inherited project such as this I
would suggest reading the date() documentation as a first step; it is
not very long since the package is simple.
You want the date.mdy function, which is more straightforward than
strptime (with less capabilities of course).
Terry Therneau
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