sort array by field

function sortByDate( a, b ) {
  if ( a.created_at < b.created_at ){
    return -1;
  }
  if ( a.created_at > b.created_at ){
    return 1;
  }
  return 0;
}

myDates.sort(sortByDate);//myDates is not sorted.

function cmp($a, $b)
{
    return strcmp($a["title"], $b["title"]);
}

usort($array, "cmp");