gistfile1.txt

  $dates = array(
    '2014-08','2014-09','2014-11','2014-12','2015-02');
  function InactiveMonths($dates) {
    sort($dates);
    $start = min($dates);
    $stop = max($dates);
    list($firstYear,$firstMonth) = explode('-',$start,2);
    list($lastYear,$lastMonth) = explode('-',$stop,2);
    $m = $firstMonth;
    for($y=(int)$firstYear;$y<=(int)$lastYear;$y++) {
      while(($y<$lastYear&&$m<=12) || ($y==$lastYear&&$m<=$lastMonth)) {
        $YM = sprintf('%d-%02d',$y,$m);
        echo $YM.' '.(in_array($YM,$dates)?'Active':'Inactive').'<br />';
        $m++;
      }
      $m = 1;
    }
  }
  InactiveMonths($dates);