$string = '2019-03-17 19:10:30';
$obj = new stdClass;
$obj->created_at = $string;
$collection = [$obj];
foreach ($collection as $k => &$v) {
$collection[$k]->created_at = strtotime($v->created_at);
}
//var_dump($collection);
или
$string = '2019-03-17 19:10:30';
$obj = new stdClass;
$obj->created_at = $string;
$collection = [$obj];
array_walk($collection, function (&$item, $key) {
$item->created_at = strtotime($item->created_at);
});
//var_dump($collection);
Или в вашем случае
public function viewArchives()
{
$data = Archive::select('created_at')->get();
foreach ($data as $k => &$v) {
$v->created_at = strtotime($v->created_at);
}
return view('view.archives', compact('data'));
}
или
public function viewArchives()
{
$data = Archive::select('created_at')->get();
array_walk($data, function (&$item, $key) {
$item->created_at = strtotime($item->created_at);
});
return view('view.archives', compact('data'));
}
Это хорошее место для использования array_walk()
функция.