Question

我有按国家/地区划分城市列表的代码：

<?php
$pdo = new PDO(...);
$cities = $pdo->query('SELECT `city`, `country` FROM `cities` ORDER BY `id` ASC');
$cities->execute();
$data = array();
foreach($cities as $row) {
$data[$row['country']][] = $row['city'];
}
foreach($data as $country){
echo "<optgroup label='{$country}'>";
foreach($country as $city){
echo "<option value='{$city}'>{$city}</option>";
}
echo "</optgroup>";
}
?>

我在需要的地方获得了optgroups，但是使用了“Array”而不是值

Answer 1

那是因为$country是一个数组。你想要主数组元素的键。你可以用这个来实现：

foreach($data as $country => $cities){
echo "<optgroup label='{$country}'>";
  foreach($cities as $city){
  echo "<option value='{$city}'>{$city}</option>";
  }
echo "</optgroup>";
}

通过这种方式，您也可以获取密钥。你的数组是这样的：

$data = array(
  "Spain" => array(
    "Madrid",
    "Barcelona",
    "Valencia"),
  "UK" => array(
     "London",
     "Oxford"));

所以你试图在你的脚本中访问它（第一次迭代）：

echo array(
    "Madrid",
    "Barcelona",
    "Valencia");

哪个不行（它会打印数组）。相反，您想要访问“西班牙”键，可以访问该键，如下所示：

 foreach ($smth as $Key => $Value)

划分foreach不能正常工作

1 个答案: