如果变量有重复，那么PHP是否只显示第一个实例？

Question

我创建了一个mysql表，其中包括这些行和值：

   category | item_name
   ======================= 
   Dinner   |  Lobster
   Dinner   |  Pizza
   Lunch    |  Sandwich
   Lunch    |  Soup
   Lunch    |  Salad
  -------------------------

然后查询数据库，结果放在一个数组"$menu_selected“中。我循环通过"$menu_selected“来显示结果。

    foreach($menu_selected as $m):
           echo $category = $m->category . "<br>";
           echo $item_name = $m->item_name . "<br><br>";
    endforeach;

输出：

    Dinner
    Lobster

    Dinner
    Pizza

    Lunch
    Sandwich

    Lunch
    Soup

    Lunch
    Salad

我如何过滤PHP中的类别，这样它就不会只回显每个类别的第一个实例？类别行值并不总是为“晚餐”或“午餐会”，我希望能够回显这个类别，而不将其与常量进行比较，比如if($category =‘晚餐’){}。我花了一周的时间研究，却搞不清楚。任何人的帮助都将不胜感激。

我希望输出如下所示：

 **Dinner**
 Lobster
 Pizza
 Sandwich

 **Lunch**
 Sandwich
 Soup
 Salad

Answer 1

确保在查询中按类别订购。然后，只需在循环之外添加一个$category变量，如果该变量已更改，则输出标头。

$category = '';
foreach($menu_selected as $m) {
     if ($m->category != $category) {
        echo "**$m->category** <br>";
        $category = $m->category;
     }
     echo $m->category . "<br>";
     echo $m->item_name . "<br><br>";
}

Answer 2

只需使用2预测法。第一类为第二类，第二类为物品

foreach($menu_selected as $m1):
       echo $category = $m1->category . "<br>";        
    foreach($menu_selected as $m):
       echo $item_name = $m->item_name . "<br><br>";
            if ($m->category != $m1->category) 
                    {
                      break;
                    }
    endforeach;
endforeach;

Answer 3

$cat_item_array = ARRAY();

foreach($menu_selected as $m) {
    if (!isset($cat_item_array[$m->category])) {
     $cat_item_array[$m->category] = $m->item_name;
     echo "found new category: ".$m->category . " (Added item: ".$m->item_name.")<br>";
     continue;
   }
    $cat_item_array[$m->category] = $m->item_name;
    echo "Added item ".$m->item_name." to category ".$m->category.".<br><br>";
}

print '<pre>'; var_dump($cat_item_array); print '</pre>';