Question

    $students = array (
     256 => array ('name' => 'Jon', 'grade' => 98.5),
     2 => array ('name' => 'Vance', 'grade' => 85.1),
     9 => array ('name' => 'Stephen', 'grade' => 94.0),
     364 => array ('name' => 'Steve', 'grade' => 85.1),
     68 => array ('name' => 'Rob', 'grade' => 74.6)
     );

 function grade_sort($x,$y){
  return ($x['grade'] < $y['grade']);
  }
uasort ($students, 'grade_sort');

i am a new learner of php,i can’t understand the above code well. could i change this return ($x['grade'] < $y['grade']); to return $x < $y; if not, why? thank you

Answer 1

could i change this return ($x['grade'] < $y['grade']); to return $x < $y;?

No. $x and $y will be one of the arrays inside $students.
E.g. $x may be array('name' => 'Jon', 'grade' => 98.5)
and $y may be array('name' => 'Vance', 'grade' => 85.1).
So return $x < $y doesn’t make sense.

That code isn’t very good though. The comparison function grade_sort takes two elements at a time and should return 0 if both elements are considered equal, a negative number if the first is lower and a positive number if the second lower. Yours returns true or false. The correct code would be:

function grade_sort($x, $y){
    return $y['grade'] - $x['grade'];
}
uasort($students, 'grade_sort');

uasort simply keeps calling this function with two different elements until it is satisfied it knows which element is larger than which and has sorted them all.