foreach ($og_groups as $k=>$v) {
  echo $og_groups[$k]['nid'];
  echo $og_groups[$k]['is_admin'];
  if ($og_groups[$k]['is_admin'] == 1) {
     $collector[] = $k;
  }
}

foreach ($og_groups as $k=>$v) {
  if ($v['is_admin'] == 1) {
     $collector[] = $k;
  }
}