划分foreach不能正常工作

Question

I have the code for dividing the list of cities by country:

<?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>";
}
?>

I get optgroups where I need but with the word "Array" instead of the value

Answer 1

That's because $country is an array. You want the key of that element of the main array. You can achieve that with this:

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

In this way you are also fetching the keys. Your array is like this:

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

So you were trying to access this in your script (for the first iteration):

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

Which wouldn't work (it would print Array). Instead, you want to access the "Spain" key, which can be accessed writting the foreach like:

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