Question

How can I get the same day of the same ISO-8601 week number but in the previous year using php?

I am familiar with extracting this soft of information from a time stamp. Is there a built-in way for me to go from day of week, week of year and year to time stamp?

Answer 1

You can use the combination of both date and strtotime like so:

// get the timestamp
$ts = strtotime('today');

// get year, week number and day of week
list($year, $week, $dow) = explode('-', date('Y-W-N', $ts));

// use the "YYYY-WXX-ZZ" format    
$format = ($year - 1) . "-W$week-$dow";
echo date('Y-m-d', strtotime($format)), PHP_EOL;