Arithmetic operations on dates ?

Michael D Mays michael.rr at mdmays.com
Sat Feb 26 07:02:45 EST 2005


Use the dateItem format of the date:

Convert your date to date items.
   convert myDate to dateItems
Now add your time increments to the appropriate item
   add 17 to item 5 of myDate -- hours
   add 3 to item 4 of myDate -- days
Then convert to dateItems again
   convert myDate to dateItems
Convert back to the date format you were using

To increment by weeks just add or subtract 7 days, item 3 of the 
dateItems.

To increment by months just add the number of months to item 2 of the 
dateItems.

Your February problem will be taken care of automatically if you are 
incrementing by the number of months.

Use seconds only when you want to know how many days are between two 
dates.
  put (dateInSeconds1-dateInSeconds2)/(86400) into theDaysInBetween

Using item 7 of the dateItems allows you to calculate dates such as 
'the second Monday of March.'

And so on.

Michael

On Feb 26, 2005, at 4:55 AM, jbv wrote:

> Hi revolutionaries,
>
> What is the best way to make artithmetic
> operations on dates ? For instance I have
> a list of events stored with the date & time
> of occurence, and I'd like to quickly pick
> up those that took place during the last 17
> hours, or the last 3 days, or the last 7 weeks
> or the last 19 months...
>
> I know this can be done with SQL but I don't
> want to set up a database just for that...
> The best thing I came up with is to convert each
> event date into seconds, subtract the amount of
> seconds of the interval of time, and then pick up
> all items greater than that...
> But I have the feeling that computing the interval
> in seconds might get tricky when there's a february
> 29 in it (for instance)...
>
> Any better idea ?
> Thanks,
> JB
>
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