php usort with subarrays

Question

I am trying to sort array with usort, but it doesn't work, What am i doing wrong?

$tmp = array();
$tmp[] = array(
  'x' => 0.000123
);
$tmp[] = array(
  'x' => 0.000120
);
$tmp[] = array(
  'x' => 0.000333
);

usort($tmp, function ($a, $b) {
  return $b['x'] - $a['x'];
});

print_r($tmp);

Answer 1

$tmp = array();
$tmp[] = array(
    'x' => 0.000123
);
$tmp[] = array(
    'x' => 0.000120
);
$tmp[] = array(
    'x' => 0.000333
);

usort($tmp, function ($a, $b) {
    $a = $a['x'];
    $b = $b['x'];
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
});

Try this one