PHP: Loop through all weeks in a date range (last 2 years)? - php

Question

I like to iterate through all weeks in a date range that spawns 2 years. Starting at the current week number two years ago, until the current week number this year.
The problem is that a year can either have 52 weeks or 53 weeks, for example:
2015 had 53 weeks (the 53th was from 2015-12-28 till 2016-01-03)
2016 had 52 weeks (the 52th was from 2016-12-26 till 2017-01-01)
So this is currently my php code:
# start with the current week 2 years ago
$year = date("Y") - 2;
$week = (int) date("W"); // (int) removes leading zero for weeks < 10
$endYear = date("Y");
$endWeek = (int) date("W");
# iterate through all weeks until now
do {
echo $week. " of ". $year;
$week++;
if ($week > 52) { // or greater 53 ?????????????
$year ++;
$week = 1;
}
}
while ($year < $endYear || $week < $endWeek);

Answer 1

Instead of trying to keep track of the bounds, let PHP do it for you.
$start = new DateTime('-2 years');
$end = new DateTime();
$interval = new DateInterval('P1W');
$period = new DatePeriod($start, $interval, $end);
foreach ($period as $date) {
echo $date->format('W') . " of ". $date->format('Y') . "\n";
}
Demo

Answer 2

With the help of Ross Wilson and John Conde I found a solution:
$now = new DateTime;
$from = (new DateTime)->setISODate($now->format('Y') - 2, $now->format('W'));
$from->modify("thursday this week"); // see ISO 8601
while($from < $now) {
echo $from->format('W Y').'<br />';
$from->modify("+1 week");
}
It is important so set the week day to thursday, because according to ISO 8601, the week "belongs" to the year which still contains the thursday.

Answer 3

You could use DateTime and setISODate for something like this:
$now = new DateTime;
$from = (new DateTime)->setISODate($now->format('Y') - 2, $now->format('W'));
while($from < $now) {
echo $from->format('W Y').'<br />';
$from->modify("1 week");
}
Hope this helps!