Accessing lower values of multilevel array in PHP

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I have a PHP array of objects and would like to get all the post_id values easily. I have looked into things like array_values and am not really sure what to do with this. Is the best way to just use a for loop and add each post_id to another array with all the post ids?

Thanks for the help!

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[0] => stdClass Object
    (
        [post_id] => 70242
        [image_id] => 70244
        [large_image] => 0
    )

[1] => stdClass Object
    (
        [post_id] => 70327
        [image_id] => 70339
        [large_image] => 1
    )

[2] => stdClass Object
    (
        [post_id] => 70017
        [image_id] => 70212
        [large_image] => 1
    )

EDIT:
I am getting this array from a WordPress db call: 

$q = <<<SQL
    SELECT post_id, image_id, large_image
    FROM $homepage_db
    ORDER BY position;
SQL;

$results = $wpdb->get_results($q);

And then $results is the array above

Post Views: 3

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3 comments

  2. using foreach

    $post_ids = array();
foreach($arr as $e) {
  $post_ids[] = $e->post_id;
}

    using array_map

    $post_ids = array_map('get_post_id', $arr);
function get_post_id($e) {
  return $e->post_id;
}

    I prefer foreach in this case

  3. Easy. Use array_map. Code below; used JSON for your data to test & demonstrate the concept while retaining your example structure:

    //  Set the JSON string for this example.
$json_string = <<<EOT
[
    {
        "post_id": "70242",
        "image_id": "70244",
        "large_image": "0"
    },
    {
        "post_id": "70327",
        "image_id": "70339",
        "large_image": "1"
    },
    {
        "post_id": "70017",
        "image_id": "70212",
        "large_image": "1"
    }
]
EOT;

// Decode the JSON string as any array.
$json_string_decoded = json_decode($json_string);

// Use array_map to return an array telling you what items have 'distancia'.
$results = array_map(function($value) {
    return $value->post_id;
  }, $json_string_decoded);

// Dump the array to view the contents.
echo '<pre>';
print_r($results);
echo '</pre>';

    And the dumped output would be:

    Array
(
    [0] => 70242
    [1] => 70327
    [2] => 70017
)