php实现按照权重随机排序数据的方法

<?php   

/**  

 * @param array $weight 权重  例如array('a'=>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;   

?>