Calculating days of week given a week number

Question

Given a week number, e.g. date -u +%W, how do you calculate the days in that week starting from Monday?

Example rfc-3339 output for week 40:

2008-10-06
2008-10-07
2008-10-08
2008-10-09
2008-10-10
2008-10-11
2008-10-12

Answer 1

this page has information which may be helpful. It includes example code in 'C'

Answer 2

PHP

$week_number = 40;
$year = 2008;
for($day=1; $day<=7; $day++)
{
    echo date('m/d/Y', strtotime($year."W".$week_number.$day))."\n";
}

---

Below post was because I was an idiot who didn't read the question properly, but will get the dates in a week starting from Monday, given the date, not the week number..

In PHP, adapted from this post on the PHP date manual page:

function week_from_monday($date) {
    // Assuming $date is in format DD-MM-YYYY
    list($day, $month, $year) = explode("-", $_REQUEST["date"]);

    // Get the weekday of the given date
    $wkday = date('l',mktime('0','0','0', $month, $day, $year));

    switch($wkday) {
        case 'Monday': $numDaysToMon = 0; break;
        case 'Tuesday': $numDaysToMon = 1; break;
        case 'Wednesday': $numDaysToMon = 2; break;
        case 'Thursday': $numDaysToMon = 3; break;
        case 'Friday': $numDaysToMon = 4; break;
        case 'Saturday': $numDaysToMon = 5; break;
        case 'Sunday': $numDaysToMon = 6; break;   
    }

    // Timestamp of the monday for that week
    $monday = mktime('0','0','0', $month, $day-$numDaysToMon, $year);

    $seconds_in_a_day = 86400;

    // Get date for 7 days from Monday (inclusive)
    for($i=0; $i<7; $i++)
    {
        $dates[$i] = date('Y-m-d',$monday+($seconds_in_a_day*$i));
    }

    return $dates;
}

Output from week_from_monday('07-10-2008') gives:

Array
(
    [0] => 2008-10-06
    [1] => 2008-10-07
    [2] => 2008-10-08
    [3] => 2008-10-09
    [4] => 2008-10-10
    [5] => 2008-10-11
    [6] => 2008-10-12
)

Answer 3

This calculation varies largely depending on where you live. For example, in Europe we start the week with a Monday, in US Sunday is the first day of the week. In UK week 1 is on Jan 1, others countries start week 1 on the week containing the first Thursday of the year.

You can find more general information at http://en.wikipedia.org/wiki/Week#Week_number

Answer 4

If you've got Zend Framework you can use the Zend_Date class to do this:

require_once 'Zend/Date.php';

$date = new Zend_Date();
$date->setYear(2008)
     ->setWeek(40)
     ->setWeekDay(1);

$weekDates = array();

for ($day = 1; $day <= 7; $day++) {
    if ($day == 1) {
     // we're already at day 1
    }
    else {
     // get the next day in the week
     $date->addDay(1);
    }

    $weekDates[] = date('Y-m-d', $date->getTimestamp());
}

echo '<pre>';
print_r($weekDates);
echo '</pre>';

Answer 5

This function will give the timestamps of days of the week in which $date is found. If $date isn't given, it assumes "now." If you prefer readable dates to timestamps, pass a date format into the second parameter. If you don't start your week on Monday (lucky), pass in a different day for the third parameter.

function week_dates($date = null, $format = null, $start = 'monday') {
  // is date given? if not, use current time...
  if(is_null($date)) $date = 'now';

  // get the timestamp of the day that started $date's week...
  $weekstart = strtotime('last '.$start, strtotime($date));

  // add 86400 to the timestamp for each day that follows it...
  for($i = 0; $i < 7; $i++) {
    $day = $weekstart + (86400 * $i);
    if(is_null($format)) $dates[$i] = $day;
    else $dates[$i] = date($format, $day);
  }

  return $dates;
}

So week_dates() should return something like...

Array ( 
  [0] => 1234155600 
  [1] => 1234242000 
  [2] => 1234328400 
  [3] => 1234414800 
  [4] => 1234501200
  [5] => 1234587600
  [6] => 1234674000
)

Answer 6

i found a problem with this solution. had to zero pad the weeknumber else was breaking. my solution looks like this now..

$week_number = 40; $year = 2008; for($day=1; $day<=7; $day++) { echo date('m/d/Y', strtotime($year."W".str_pad($week_number,2,'0',STR_PAD_LEFT).$day))."\n"; }

Answer 7

For those looking for the days of the week given the week number (1-52) Starting from a sunday then here is my little work around. Takes into account checking the week is in the right range and pads the values 1-9 to keep it all working.

---

$week = 2; $year = 2009;

$week = (($week >= 1) AND ($week <= 52))?($week-1):(1);

$dayrange = array(7,1,2,3,4,5,6);

for($count=0; $count<=6; $count++) { $week = ($count == 1)?($week + 1): ($week); $week = str_pad($week,2,'0',STR_PAD_LEFT); echo date('d m Y', strtotime($year."W".$week.($dayrange[$count]))); }

Answer 8

hi !, any chance to have the same in AS3 ?

I came from Python programming where functions in Date class are very rich, so i have some problem in Flex/as3 :

here where i go :

I search a way (fonction or class or method) to get the seven day for a weeknumber.

For example, myfunction(34) will return : 2009-08-17 2009-08-18 2009-08-19 2009-08-20 2009-08-21 2009-08-22 2009-08-23

any chance that somebody always did that ?

Thank you for help or read me !

Answer 9

$week_number = 40; $year = 2008;

for($day=1; $day<=7; $day++) { echo date('m/d/Y', strtotime($year."W".$week_number.$day))."\n"; }

THIS WILL FAIL IF $week_number IS LESS THAN 10.

//============Try this================//

$week_number = 40; $year = 2008;

if($week_number < 10){ $week_number = "0".$week_number; }

for($day=1; $day<=7; $day++) { echo date('m/d/Y', strtotime($year."W".$week_number.$day))."\n"; }

//==============================//