php按照权重随机

10,'b'=>20,'c'=>50)  
 * @return string key   键名   
 */  
function roll($weight = array()) {   
	$roll = rand ( 1, array_sum ( $weight ) );   
	$_tmpW = 0;   
	$rollnum = 0;   
 	foreach ( $weight as $k => $v ) {   
		$min = $_tmpW;   
	 	$_tmpW += $v;   
	 	$max = $_tmpW;   
	 	if ($roll > $min && $roll <= $max) {   
	 		$rollnum = $k;   
	 		break;   
	 	}   
	}   
 	return $rollnum;   
}   
  
$row=roll(array('a'=>10,'b'=>20,'c'=>50));   
echo $row;   
?>