[R] Rounding in date.mdy from library(date)
Kurt.Hornik at ci.tuwien.ac.at
Tue Jan 4 09:22:38 CET 2000
>>>>> Thomas Lumley writes:
> On Mon, 3 Jan 2000, BXC (Bendix Carstensen) wrote:
>> The date library contains a function date.mdy that converts a number
>> D to the date (month,date,year as a list) at D days after 1 Jan 1960.
>> This a convention that fits in with SASs.
>> The logic would be that the result was the date at D days after
>> 1 Jan 1960 00:00:00 (which is a POINT in time as opposed to a date which
>> is an interval), so that any D with 2<=D<3 was rounded to 3 Jan 1960
>> and so on. This is because at any time D days (i.e. D*24h) after
>> 1.1.1960:00:00 with 2<=D<3 we would call the date "3 Jan 1960".
> I think the date package is only intended to handle integers. This is
> partly because date.mdy is _not_ a function for converting numbers to
> dates, it is a function for converting dates to a printable form.
> If you look at as.date() the truncation is already done there,
>  1Jan60
>  1Jan60
> so a bona fide date object will always have an integer as the time since
> 1/1/1960. In that sense the workaround is to only use date.mdy on dates,
> not on numbers.
> I agree that it might be worth extending date to allow times in
> addition to dates (in which case it probably would have to have
> information on time zones as well). The tricky part would be parsing
> time information in character form, but there is probably GNU code for
If you want time information as well, you can use package chron (which
does not use time zones, however).
It would certainly be nice to have something for handling dates/times
which can use strftime(3) formats. And of course, it would make sense
to build something around a data type modelled around struct tm.
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