Re: Get Start Date of a Week Number

And is that any easier to understand or trust than

p IsoWkdayNum b export
d IsoWkdayNum pi 10i 0
d date d const

d d s 10i 0

/free

exec sql values dayofweek_iso(date) into :d;

return d;

/end-free
p e


p IsoWeekNum b export
d IsoWeekNum pi 10i 0
d date d const

d w1 s 10i 0

/free

exec sql values week_iso(date) into :w1;

return w1;

/end-free
p e


Rob Berendt
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From: John E <whattssonn@xxxxxxxxx>
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Date: 12/03/2014 07:17 AM
Subject: Re: Get Start Date of a Week Number
Sent by: "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx>



From http://nl.wikipedia.org/wiki/Weeknummer (which is in dutch) :

To calculate the ISO weekday (1=monday) for a given date:

p IsoWkdayNum b export
d IsoWkdayNum pi 10i 0
d date d const

d d s 10i 0

/free

d = %diff(date:d'1970-01-04':*d);

if d < -6;
return 7 - %rem(%abs(d) - 7 : 7);
elseif d < 0;
return 7 + d;
endif;

d = %rem(d : 7);

if d = 0;
return 7;
endif;

return d;

/end-free
p e


To calculate the ISO weeknumber for a given date (using the previous
IsoWkdayNum) :
The year must be from 1584 to 9998, else it returns 0.

p IsoWeekNum b export
d IsoWeekNum pi 10i 0
d date d const

d y s 10i 0
d m s 10i 0
d d s 10i 0
d w1 s 10i 0
d w2 s 10i 0
d wd1 s 10i 0
d wd2 s 10i 0
d wd3 s 10i 0
d wd4 s 10i 0
d wd5 s 10i 0
d x s 10i 0

/free

// http://nl.wikipedia.org/wiki/Weeknummer --------------------

y = %subdt(date:*y);

if y < 1584
or y > 9998;
return 0;
endif;

m = %subdt(date:*m);
d = %subdt(date:*d);

// UK02
w1 = %div(%diff(date:%date(y*10000+104:*iso):*d):7);

// UK03
wd1 = IsoWkdayNum(date);

// UK04
wd2 = wd1 - %rem(%diff(date:%date((y-1)*10000+104:*iso):*d):7);
if wd2 < 1;
wd2 = wd2 + 7;
endif;

// UK06
w2 = %div(%diff(%date((y-1)*10000+1231:*iso)
:%date((y-1)*10000+104:*iso):*d)
:7);

// UK07
wd3 = wd1 - %rem(%diff(date:%date((y-1)*10000+1231:*iso):*d):7);
if wd3 < 1;
wd3 = wd3 + 7;
endif;

// UK08
x = %diff(date:%date(y*10000+104:*iso):*d);
if x < 0;
wd4 = wd1 - x;
if wd4 > 7;
wd4 = wd4 - 7;
endif;
else;
wd4 = wd1 - %rem(x:7);
if wd4 < 1;
wd4 = wd4 + 7;
endif;
endif;

// UK09
wd5 = wd1 + %rem(%diff(%date((y+1)*10000+104:*iso):date:*d):7);
if wd5 > 7;
wd5 = wd5 - 7;
endif;

// UK11
if m = 1
and d >= 1
and d <= 3;
if wd1 < wd4;
return 1;
else;
// UK10
if wd3 < wd4;
return 1;
elseif wd3 < wd2;
return w2 + 2;
endif;
return w2 + 1;
endif;
elseif m = 12
and d >= 29
and d <= 31
and wd1 < wd5;
return 1;
elseif wd1 < wd4;
return w1 + 2;
endif;

return w1 + 1;

/end-free
p e


The code above is tested, and is correct.


On Wed, Nov 26, 2014 at 3:52 PM, Brian <belstsrv@xxxxxxxxx> wrote:

Hello All,

I have the need to get the date of the first day of the week based on a
week number. I've looked thorough lots of date functions and can't seem

to

see a way to get the date of the first day of the week for a particular
week number. Maybe I need a multi-step process, but I am just

struggling

to see it.

The date can be based off Sunday or whatever arbitrary day could be
considered as the first day of the week, if that helps.

The data is planning data so I really just need to show it as a quantity
along with a date, but the date needs derived from a week number.

As an example, if I had week number of 1, the date might be 12/29/2014,
week 2 would give me 1/5/2015 and so on.

Can anyone provide some suggestions on a method to get to a date based

off

the week number?

Thank you.
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