FONCTION ALÉATOIRE QUI PREND EN COMPTE LES PROBABILITÉS ...

<?php
   //ProbaRand();
   function ProbaRand()
   {
      $arg_list = func_get_args();
      $tablo = array();
      $start = 0;
      foreach($arg_list as $arg_curr)
      {
         if(!is_array($arg_curr)){return (false);}
         $tempo = array();
         list($tempo['name'], $tempo['probability']) = $arg_curr;
         $tempo['start'] = $start;
         $tempo['end'] = $start + $tempo['probability'];
         $start += $tempo['probability'];
         array_push($tablo, $tempo);
      }
      $result = mt_rand(0, 1000)/1000;
      foreach($tablo as $once)
      {
         if($result >= $once['start'] AND $result <= $once['end'])
         {
            return($once['name']);
         }
      }
   }
  //Par exemple : ProbaRand(array('A', 0.1), array('B', 0.2), array('C', 0.3), array('D', 0.4));
?>