Mengambil Data Bulan dari Range

<?php
function getDates($sDate, $eDate=NULL){
    $tgl_libur = is_array($tgl_libur) ? $tgl_libur : array($tgl_libur);
    $eDate = $eDate ? $eDate : date("Y-m-d");
    $day = 86400;
    if(strtotime($sDate)>strtotime($eDate)){
        $startDate = strtotime($eDate);
        $endDate = strtotime($sDate);
    }else{
        $startDate = strtotime($sDate);
        $endDate = strtotime($eDate);
    }
    $numDays = round(($endDate - $startDate) / $day) + 1;
    $days = array();
    for ($i = 0; $i < $numDays; $i++) {
        $days[] = date("Y-m-d", ($startDate + ($i * $day)));
    }
    return $days;
}

$ti1 = $_GET['month_start'];
$ti2 = $_GET['month_end'];
$tgls = getDates($ti1,$ti2);
for($i=0;$i<=count($tgls)-1;$i++)
    $data_bulan[substr($tgls[$i],0,7)] = $i;
$data_bulan = array_keys($data_bulan);
print_r($data_bulan);
?>