Did I mention I like date math? Brain-twisting stuff.
On Tue, May 8, 2018 at 5:14 PM, Ted Roche <tedro...@gmail.com> wrote:
> How about:
>
> FUNCTION olddate(thedate, offset)
> * parameters:
> * the date: the source date
> * offset number of years offset, positive or negative
> * returns: the nearest date that is the same day of week as the source date
>
> LOCAL thediff, theoffset
> thediff = DOW(thedate) - DOW(GOMONTH(thedate, offset*12))
> theoffset = IIF(ABS(thediff)>3, 7-SIGN(thediff)*(thediff), thediff)
> RETURN GOMONTH(thedate, offset*12)+theoffset
>
> ABS() only picks up the high end of the date difference, 4,5,6
> SIGN() toggles whether you add or subtract the difference (minus a
> minus is a plus)
>
>
> On Tue, May 8, 2018 at 5:03 PM, Ted Roche <tedro...@gmail.com> wrote:
>> An ICASE might do it.
>>
>> Basically the idea is get the day number (DOW) of the current date,
>> like 2 for Tuesday if SET FDOW is 1 ("the first day of the week is
>> Monday")
>>
>> Then create a new date with GOMONTH() and get the day number of that,
>> some number 1 through 7. So if the new date is a five, I want to go
>> back 3 to get to 2. Similarly, if it's a 6, I want to go forward 3 to
>> get to the next, closest 2.
>>
>> So, you want to find the nearest matching day number: they're either
>> the same day, so zero offset, or the matching day number are 1,2,3
>> days earlier or later.
>>
>> so you take the difference between the original date and the new date.
>> if the absolute difference is 3 or less, that's your offset and you
>> use that to move the new date to the matching day number.
>>
>> If the difference is -4, -5, -6 or 4, 5, 6 days, you need to look to
>> the next/previous weeks' matching day number, hence the magic 7
>> number.
>>
>>
>> On Tue, May 8, 2018 at 3:39 PM, Richard Kaye <rk...@invaluable.com> wrote:
>>> Or an ICASE? (I haven't quite wrapped my head around what you're doing
>>> there but it seems like there are 3 states?)
>>>
>>> m.theOffset=ICASE(theDiff>3, 7-m.theDiff,theDiff<-3, 7+m.theDiff, m.theDiff)
>>>
>>> --
>>>
>>> rk
>>>
>>> -----Original Message-----
>>> From: ProfoxTech <profoxtech-boun...@leafe.com> On Behalf Of Ted Roche
>>> Sent: Tuesday, May 08, 2018 3:25 PM
>>> To: profoxt...@leafe.com
>>> Subject: Re: Fun with date calculations in VFP
>>>
>>> GOMONTH() just moves back to 2/28 on years that don't have a 2/29, so
>>> your olddate({^2016-02-29},-2) gives you the previous Tuesday,
>>> 2/24/2014.
>>>
>>> Hmmm. That's an OBO. It goes back 4 instead of forward 3. I think the
>>> nearest date ought to be 2014-03-03
>>>
>>> Ah, if thediff = -4, it remains -4. That's a bug. Add the second line
>>> below after the first:
>>>
>>> m.theOffset=IIF(theDiff>3, 7-m.theDiff, m.theDiff)
>>> m.theOffset=IIF(theDiff<-3, 7+m.theDiff, m.theDiff)
>>>
>>> I know there's a better algorithm, likely involving MOD() or CEILING()
>>> or FLOOR() but it's escaping me at the moment.
>>>
>>> There's 49 combinations of original date = (1,2,3,4,5,6,7) and
>>> resultant date = (1,2,3,4,5,6,7) and the offset should come out as
>>> {-3,-2,-1,0,1,2,3} , but I'm drawing a blank. Anyone? Beuller?
>>>
>>>
>>>
>>> On Tue, May 8, 2018 at 2:15 PM, Richard Kaye <rk...@invaluable.com> wrote:
>>>> Ted's solution works just fine. What I didn't test yet is using leap day
>>>> itself as the starting point. Hmmm.....
>>>>
>>>> **************************************
>>>> * Program: datestuff3.prg
>>>> * Date: 05/08/2018 11:09 AM
>>>> * VFP Version: Visual FoxPro 09.00.0000.7423 for Windows
>>>> * Notes:
>>>> **************************************
>>>> ACTIVATE SCREEN
>>>> CLEAR
>>>> ? [Today: ]+CHR(9)+CHR(9)
>>>> ?? DATE()
>>>> ?? CHR(9)+CDOW(DATE())
>>>> ? [Same day last year: ]
>>>> ?? olddate(DATE(),-1)
>>>> ?? CHR(9)+CDOW(olddate(DATE(),-1))
>>>> ? [Same day 2 years ago: ]
>>>> ?? olddate(DATE(),-2)
>>>> ?? CHR(9)+CDOW(olddate(DATE(),-2))
>>>> ? [Same day 3 years ago: ]
>>>> ?? olddate(DATE(),-3)
>>>> ?? CHR(9)+CDOW(olddate(DATE(),-3))
>>>> ? [Same day 10 years ago: ]
>>>> ?? olddate(DATE(),-10)
>>>> ?? [ ]+CDOW(olddate(DATE(),-10))
>>>> ? [Yesterday: ]+CHR(9)
>>>> ?? DATE()-1
>>>> ?? CHR(9)+CDOW(DATE()-1)
>>>> ? [Same day last year: ]
>>>> ?? olddate(DATE()-1,-1)
>>>> ?? CHR(9)+CDOW(olddate(DATE()-1,-1))
>>>> ? [Same day 2 years ago: ]
>>>> ?? olddate(DATE()-1,-2)
>>>> ?? CHR(9)+CDOW(olddate(DATE()-1,-2))
>>>> ? [Same day 3 years ago: ]
>>>> ?? olddate(DATE()-1,-3)
>>>> ?? CHR(9)+CDOW(olddate(DATE()-1,-3))
>>>> ? [Same day 10 years ago: ]
>>>> ?? olddate(DATE()-1,-10)
>>>> ?? [ ]+CDOW(olddate(DATE()-1,-10))
>>>> ? [Tomorrow: ]+CHR(9)
>>>> ?? DATE()+1
>>>> ?? CHR(9)+CDOW(DATE()+1)
>>>> ? [Same day last year: ]
>>>> ?? olddate(DATE()+1,-1)
>>>> ?? CHR(9)+CDOW(olddate(DATE()+1,-1))
>>>> ? [Same day 2 years ago: ]
>>>> ?? olddate(DATE()+1,-2)
>>>> ?? CHR(9)+CDOW(olddate(DATE()+1,-2))
>>>> ? [Same day 3 years ago: ]
>>>> ?? olddate(DATE()+1,-3)
>>>> ?? CHR(9)+CDOW(olddate(DATE()+1,-3))
>>>> ? [Same day 10 years ago: ]
>>>> ?? olddate(DATE()+1,-10)
>>>> ?? [ ]+CDOW(olddate(DATE()+1,-10))
>>>>
>>>> FUNCTION oldDate(theDate AS Date, offset AS Integer)
>>>> * compliments of Ted Roche
>>>> * parameters: thedate: date to start from
>>>> * offset: number of years offset, positive or negative
>>>> * returns: nearest date to the offset that falls on the same day of the
>>>> week
>>>> LOCAL m.theDiff, m.theOffset
>>>> m.theDiff=DOW(m.theDate)-DOW(GOMONTH(m.theDate, m.offset*12))
>>>> m.theOffset=IIF(theDiff>3, 7-m.theDiff, m.theDiff)
>>>> RETURN GOMONTH(m.theDate, m.offset*12) + m.theOffset
>>>>
>>>> ENDFUNC
>>>>
>>>> --
>>>>
>>>> rk
>>>>
>>>> -----Original Message-----
>>>> From: ProfoxTech <profoxtech-boun...@leafe.com> On Behalf Of Gene Wirchenko
>>>> Sent: Tuesday, May 08, 2018 12:46 PM
>>>> To: profoxt...@leafe.com
>>>> Subject: RE: Fun with date calculations in VFP
>>>>
>>>> At 06:27 2018-05-08, Richard Kaye <rk...@invaluable.com> wrote:
>>>>>The latter. And that was the approach I was just working through.
>>>>
>>>> What about the week every few years that you will be disregarding?
>>>>
>>>> A year has 52 weeks plus one or two days.
>>>>
>>>> [snip]
>>>>
>>>> Sincerely,
>>>>
>>>> Gene Wirchenko
>>>>
>>>>
[excessive quoting removed by server]
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