Change order of billing fields on checkout page - woocommerce

Question

I’m using the WC filter to order billing fields
It seems the filter works fine, but for unknown reasons it revert back on the fly to the default order.
add_filter("woocommerce_checkout_fields", "custom_order_fields");
function custom_order_fields($fields) {
$order = array(
"billing_first_name",
"billing_last_name",
"billing_country",
"billing_address_1",
"billing_address_2",
"billing_state",
"billing_city",
"billing_phone",
"billing_email"
);
foreach($order as $field)
{
$ordered_fields[$field] = $fields["billing"][$field];
}
$fields["billing"] = $ordered_fields;
$fields['billing_first_name']['priority'] = 10;
$fields['billing_last_name']['priority'] = 20;
$fields['billing_country']['priority'] = 30;
$fields['billing_address_1']['priority'] = 40;
$fields['billing_address_2']['priority'] = 50;
$fields['billing_state']['priority'] = 40;
$fields['billing_city']['priority'] = 70;
$fields['billing_phone']['priority'] = 80;
$fields['billing_email']['priority'] = 90;
return $fields;
}

Answer 1

How about this?
function custom_order_fields($fields) {
$order = array(
"billing_first_name",
"billing_last_name",
"billing_country",
"billing_address_1",
"billing_address_2",
"billing_state",
"billing_city",
"billing_phone",
"billing_email"
);
foreach($order as $key => $field)
{
if (!empty($fields["billing"][$field]))
$fields["billing"][$field]['priority'] = ($key + 1) * 10;
}
return $fields;
}
another solution is to build your array $order like this:
function custom_order_fields($fields) {
$order = array(
"billing_first_name" => 10,
"billing_last_name" => 20,
"billing_country" => 30,
"billing_address_1" => 40,
"billing_address_2" => 50,
"billing_state" => 60,
"billing_city" => 70,
"billing_phone" => 80,
"billing_email" => 90
);
foreach($order as $field => $priority)
{
if (!empty($fields["billing"][$field])) {
$fields["billing"][$field]['priority'] = $priority;
}
}
return $fields;
}