Get week number in month from date in PHP?

Question

I have an array of random dates (not coming from MySQL). I need to group them by the week as Week1, Week2, and so on upto Week5.

What I have is this:

Answer 1

I think this relationship should be true and come in handy:

Week of the month = Week of the year - Week of the year of first day of month + 1

Implemented in PHP you get this:

function weekOfMonth($date) {
    //Get the first day of the month.
    $firstOfMonth = strtotime(date("Y-m-01", $date));
    //Apply above formula.
    return intval(date("W", $date)) - intval(date("W", $firstOfMonth)) + 1;
}

To get weeks that starts with sunday, simply replace both date("W", ...) with strftime("%U", ...).