How to get year-sensitive calendar week ? date(“W”) gives back 52 for 1st of January

Question

As the headline says, PHP's date("W") function gives back the calendar week (for the current day). Unfortunatly it gives back 52 or 53 for the first day(s) of most years. This is, in a simple thinking way, correct, but very annoying, as January 1st of 2012 is not calendar week 52, it's NOT a calendar week of the current year. Most calendars define this as week 0 or week 52 of the previous year.

This is very tricky when you group each day of the year by their calendar week: 1st of January 2012 and 31st of December 2012 are both put into the same calendar week group.

So my question is: Is there a (native) year-sensitive alternative to PHP's date("W") ?

EDIT: I think I wrote the first version of this question in a very unclear way, so this is my edit: I'm searching for a function that gives back the correct calendar week for the first day(s) of the year. PHP's date("W") gives back 52 for the 1st of January 2012, which is "wrong". It should be 0 or null. According to official sources, the first calendar week of a year starts on the first monday of the year. So, if the first day of a year is not a monday, it's not week 1 ! It's week 0. The wikipedia article says

If 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01. If 1 January is on a Friday, Saturday or Sunday, it is in week 52 or 53 of the previous year.

This becomes tricky as the last days of the year are also in week 52/53. date("W") does not divide into current year and previous year.

INFO: The "beginning of a week" is different depending on culture and country. For example, in Northern America the week starts on SUNDAY (!). What the hell is wrong with you US people, the week simply doesn't start on Sunday ? ;) Afaik there are also countries that define Wednesday as "first day of week". — Sliq
btw a similiar issue is now the highest voted comment on PHP's date doc page: php.net/manual/de/function.date.php#106974 — Sliq

Michel Michel · Accepted Answer · 2013-12-30T16:42:43

This solution converts the excess of december to week 53 and everything in january prior to week 1 to week 0.

$w=(int)date('W');
$m=(int)date('n');
$w=$w==1?($m==12?53:1):($w>=51?($m==1?0:$w):$w);

echo "week $w in ".date('Y');

2013-12-31 ==> week 53 in 2013

2014-01-01 ==> week 1 in 2014

2015-12-31 ==> week 52 in 2015

2016-01-01 ==> week 0 in 2016

And a small test run, so you can see for yourself ;-)

$id=array(25,26,27,28,29,30,31,1,2,3,4,5,6,7,8);        
for($iy=2013;$iy<2067;++$iy){foreach($id as $k=>$v){if($k<7){$im=12;}else{$im=1;}
if($k==7){++$iy;echo '====<br>';}$tme=strtotime("$im/$v/$iy");
echo date('d-m-Y',$tme),'  * *  ';
//THE ACTUAL CODE =================
    $w=(int)date('W',$tme);
    $m=(int)date('n',$tme);
    $w=$w==1?($m==12?53:1):($w>=51?($m==1?0:$w):$w);
//THE ACTUAL CODE =================
echo '<b>WEEK: ',$w,' --- ','YEAR: ',date('Y',$tme),'</b><br>';}--$iy;
echo '----------------------------------<br>';}

How to get year-sensitive calendar week ? date(“W”) gives back 52 for 1st of January

3 Answers