Thanks Charlie. Your solution works well. That IS weird that the plain
DateDiff yields 8 weeks...
Blessings,
Graham
----- Original Message -----
From: "charlie arehart" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, January 15, 2002 3:20 PM
Subject: RE: [CFTALKTor] DateDiff question
> Well, while you'd think it should be 10, I'm more curious why it's showing
> 8, when according to the docs (which are pretty explicit about DateDiff
and
> use of the "ww" datepart for weeks) it should be 9:
>
> If interval is Week ("ww"), however, the DateDiff function returns the
> number of calendar weeks between the two dates. It counts the number of
> Sundays between date1 and date2. DateDiff counts date2 if it falls on a
> Sunday; but it doesn't count date1, even if it does fall on a Sunday.
>
> Some code demonstrates things
>
> <cfset date1="jan 14 2002">
> <cfset date2="Mar 18 2002">
> <cfoutput>
> #date1# falls on a #dayofweekasstring(dayofweek(date1))#<br>
> #date2# falls on a #dayofweekasstring(dayofweek(date2))#<br>
> Weeks between them: #datediff("ww", date1, date2)#
> </cfoutput>
>
> The result is:
>
> jan 14 2002 falls on a Monday
> Mar 18 2002 falls on a Monday
> Weeks between them: 8
>
> It reports 8, as you say, but I find that counting the number of Sundays
> between those dates, I get 9. And you want 10. :-)
>
> The mistake between 8 and 9 seems to be a bug, or a mistake in the docs (I
> think the latter, because if you simply count Mondays from Monday Jan 14,
> when you get to Mon Mar 18 you count 9. Now, you say you want 10. Here's
one
> way to get 10:
>
> Weeks between them: #ceiling(evaluate(datediff("d", date1, date2)/7))#
>
> This gets 9 with your dates, by dividing the number of days between the
> dates by 7, then the "ceiling" takes the integer part of the result (no
> fraction/remainder wanted) and raises it to the next whole number if there
> was a remainder. We don't want to round.
>
> Now, you wanted 10. I'd argue that this a semantic debate about what
> "between" means. But, from the algorithm in CF, it won't matter if you up
> the end date by a day. It still counts Sundays between the dates. In my
> code, since your second date always means "including this date", you can
> simply change the algorithm to add a day, as in:
>
> Weeks between them: #ceiling(evaluate(datediff("d", date1,
> dateadd("d",1,date2))/7))#
>
> Note that I've just slipped in a dateadd to add a day to the second date.
> This also demonstrates the reason for the ceiling. Without it, the answer
> would be 9.14285714286. And again you don't want to round down. The
ceiling
> makes it 10.
>
> Hope that helps. CF functions are really quite powerful!
>
> /charlie
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> Behalf Of Graham Faulkner
> Sent: Tuesday, January 15, 2002 1:20 PM
> To: [EMAIL PROTECTED]
> Subject: [CFTALKTor] DateDiff question
>
>
> Hi there,
>
> I have a site where I need to specify the amount of weeks a course is
> scheduled. For example, there is a course that meets every Monday night
> from January 14 until March 18. However, when I use #DateDiff("WW",
> StartDate, EndDate)# it calculates it as 8 weeks, instead of the 10 it
needs
> to be because there are classes on the start and end dates. Am I using
the
> function incorrectly? Should I be using something else to calculate this?
>
> Thanks in advance for your help.
>
> Blessings,
>
> Graham
>
> ------------------------------------------------------------
> Graham Faulkner, BBA
> President
> Global Audience Communications
>
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>
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>
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