How could I find the corresponding date for: "The monday of 2 weeks ago" "The next sunday" "The last day of the current/next/prev month ?"
Ashley
The monday of 2 weeks ago ... either now/weekday = 1 [now - 14][now - (6 + now/weekday)] The next sunday ... either now/weekday = 7 [now + 7][now + (7 - now/weekday)] The last day of the current/next/prev month ... http://www.rebol.org/view-script.r?script=date-time.r
Gregg
Giuseppe, individual date calcs are relatively easy. Designing a dialect to interpret human expressions of them is more work, though still doable. I have a number of things that do part of it, but no complete, open system I can post.
Watch for boundary issues. Here are a couple helpers that show what I mean.
set 'last-day-of-month func [date /local d] [ d: date d/day: 1 d/month: d/month + 1 d: d - 1 d ]
set 'same-day-next-month func [date /local d] [ d: date d/month: d/month + 1 if d/day < date/day [d: d - d/day] d ]
GiuseppeC
Ashley, how if I need to calculate a generic monday of N weeks AGO or sunday of N weeks in the future ?
The following code returns the dayofweek of /weeks/ ago dayofweek: 1 weeks: 2 date: either now/weekday = dayofweek [now - (7 * (weeks - 1))] [now - (((7 * (weeks - 1)) - dayofweek) + now/weekday)]
GiuseppeC
Note that this formula is dangerous when you want to filter something from a start to and date because it includes TIME! now should be changed to now/date
DideC
I have a generic calculation for dates: date-of-monday: a-date + 1 - a-date/weekday If you need a sunday, it become: date-of-sunday: a-date + 7 - a-date/weekday Then just add or remove (weeks * 7)
GiuseppeC
Interesting
Arnold
What should same-day-next-month be today?
Gregg
That would be open to interpretation on a day like today. My call, when I wrote that func, was to use the last day of the month, if the next month has less days than the target month.
Alternately, you could throw an error or return none.