PHP 정렬 알고리즘 예제에 대한 자세한 설명

<?php
  $array = $mysql->query_array($mysql->sql_select("user","userid,truename,year"," ")); //从数据库里面读出数据
  $year = array(); //设置空数组
  foreach($array as $value)
  {
    array_push($year,$value[2]); //把数据数组里面的时间数据入栈
  }
  $year = array_unique($year); //去除数组中重复的数据
  usort($year, "strnatcmp"); //将数组中的数据按自然数排序
  $num = count($year); //统计数据中数据的个数
 /*处理函数*/
 function isyear($value,$array)
 {
   $user = array(); //建立空数组
   foreach($array as $val)
   {
    if($val[2] == $value)
    {
     array_push($user,$val);
    }
   }
   return $user; //返回数组
 }
?>

<?php
for($i=0;$i<$num;$i++)
{
echo "<p class=&#39;box_user&#39;>";
echo "<p class=&#39;boxleft&#39;>{$year[$i]}届</p>";
echo  "<p class=&#39;boxright&#39;>";
$user = isyear($year[$i],$array);
foreach($user as $v)
{
echo "<span class={$v[0]}>{$v[1]}</span>";
}
echo "</p>";
echo "</p>";
}
?>

<?php
  memory_get_usage();
?>