Sort an array of arrays in PHP

gistfile1.txt

<?php

$r = array(
  array('year'=>2017,'month'=>1,'day'=>15),
  array('year'=>2017,'month'=>2,'day'=>16),
  array('year'=>2017,'month'=>2,'day'=>15),
  array('year'=>2017,'month'=>2,'day'=>14),
  array('year'=>2017,'month'=>3,'day'=>15),
  array('year'=>2017,'month'=>4,'day'=>15),
  array('year'=>2016,'month'=>5,'day'=>15),
  array('year'=>2015,'month'=>6,'day'=>15),
  array('year'=>2016,'month'=>7,'day'=>15),
  array('year'=>2014,'month'=>8,'day'=>15),
);

// Want result in descending year order, and then sorted by ascending month & day order.

usort($r, function($a, $b) {
    // First sort by year descending, swap "A" & "B" is you want asc.
    $rdiff = $b['year'] - $a['year'];
    if ($rdiff) return $rdiff;
    // then sort by month ascending, swap "A" & "B" is you want desc.
    $rdiff = $a['month'] - $b['month'];
    if ($rdiff) return $rdiff;
    // then sort by day ascending, swap "A" & "B" is you want desc.
    $rdiff = $a['day'] - $b['day'];
    return $rdiff;
});

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