Anyone got a date math routine?

[Jay R. Ashworth]

On Mon, Dec 03, 2007 at 04:29:48PM -0500, Kenneth Brody wrote:
> Quoting Jay R. Ashworth (Mon, 3 Dec 2007 15:58:08 -0500):
> >Before I write it myself, does anyone have a fuzzy age routine?  I need
> >something that can take 2 dates and 2 times, and subtract one from the
> >other, and then round, so that what I get is "32m", "6h", "3d", "2w",
> >"4M", etc.  That is, figure out what the largest unit of time is that
> >the difference can be represented in as a clipped integer, and return
> >that as a 3 character string.
> >
> >I have a design for such a routine in my head, but I figure if anyone's
> >already plowed the ground...
> >
> >If not, I'll post it here when I'm done with it.
> 
> Well, here's my first pass, off the top of my head...
> 
> Given that this is to give approximate ages anyway, this will assume:
> 
>     One year is 365.25 days.
>     One month is 1/12th of a year.
> 
> Use date/time math to get the number of seconds between the date+time.
> (Date minus date equals days.  Time minus time equals hours.)  Then,
> use the following:
> 
>     1 minute = 60 seconds
>     1 hour = 3600 seconds
>     1 day = 86,400 seconds
>     1 week = 604,800 seconds
>     1 month = 2,629,800 seconds
>     1 year = 51,557,600 seconds
> 
> You then just need to decide cutoffs.  For example, how many seconds
> do you need before switching to hours?  How many before switching to
> days?  And so on.

You return minutes until you have about 80 of them, then switch to
hours until 23, days until 6, weeks until 4, months until 11.

That's what *I* want, anyway.

> Then, divide by that unit.

Yep, that was my plan, to within delta.  I was just hoping someone'd
written the code already.  :-)

My issue -- the thing I figured would require testing, is that you
can't actually just do the days and the hours, I'm pretty sure:

You need to do the days, and convert to seconds, and then do

ENDTIME - midnight == seconds to add  

and

23:59:59 - STARTTIME = seconds to subtract

And *then* convert back.  No?

Or is that an identity, mathematically, with the way you suggested
doing it?

> Plus, are you sure you want to clip and not do some rounding at least?
> Is 51,557,599 seconds really "11 months"?

You're right; I probably need to set my cutoffs to about the 5/4 rounding
points.  Which means I need to decide *before* I convert... or use
floats internally.

Cheers,
-- jra
-- 
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