Array sorteren op datum

Array (

[groep] => 

Array ( 
 [datum] => 1194385378
 [id] => 57 
 [naam] => Angelic Layer 
) 

)

Array (
 
[groep] => 
 
Array ( 
 [datum] => 1194385378
 [id] => 57 
 [naam] => Angelic Layer 
) 
 
)

	//MENU LAST OR UPDATED INLADEN
	$sMedia = mysql_query("SELECT id, naam, path  FROM `anime_series` where id = 75 OR id = 58 or id = 57 or id = 56") 	
	or die(mysql_error());
	
	if(mysql_num_rows($sMedia) != 0) 
	{
		$i=0;
		  while ( $data = mysql_fetch_array ( $sMedia ) )
		  {
		  	 $sxe = new SimpleXMLElement($data['path'], NULL, TRUE);
		  	 $arr[$i]["id"] 		= $data["id"];
		 	 $arr[$i]["naam"]		= $data["naam"];
			 $arr[$i]["datum"]		= $sxe->serie[0]->released;
			 
			 $i++;
		  }
			function cmp($a, $b) 
			{
				return strcmp($a["datum"], $b["datum"]);
			}	  
			usort($arr,"cmp");		    
	}
	
for ($i = 0; $i <= 4; $i++) {
		$tpl->newBlock('LASTANIME');
		$tpl->assign( array(
					'SerieNaam'		=> $arr[$i]['naam'],
					'SerieUrl'		=> $arr[$i]['id'],
					'SerieDatum'	=> date("d-m-Y",(int) $arr[0]['datum'])
					)
		);
}

//MENU LAST OR UPDATED INLADEN
	$sMedia = mysql_query("SELECT id, naam, path  FROM `anime_series` where id = 75 OR id = 58 or id = 57 or id = 56") 	
	or die(mysql_error());
 
	if(mysql_num_rows($sMedia) != 0) 
	{
		$i=0;
		  while ( $data = mysql_fetch_array ( $sMedia ) )
		  {
		  	 $sxe = new SimpleXMLElement($data['path'], NULL, TRUE);
		  	 $arr[$i]["id"] 		= $data["id"];
		 	 $arr[$i]["naam"]		= $data["naam"];
			 $arr[$i]["datum"]		= $sxe->serie[0]->released;
 
			 $i++;
		  }
			function cmp($a, $b) 
			{
				return strcmp($a["datum"], $b["datum"]);
			}	  
			usort($arr,"cmp");		    
	}
 
for ($i = 0; $i <= 4; $i++) {
		$tpl->newBlock('LASTANIME');
		$tpl->assign( array(
					'SerieNaam'		=> $arr[$i]['naam'],
					'SerieUrl'		=> $arr[$i]['id'],
					'SerieDatum'	=> date("d-m-Y",(int) $arr[0]['datum'])
					)
		);
}