$i = 0;
while ( loop ) {
  $unique[i] = $field['link'];
  if(in_array($field['link'],$unique[])){
      do something
      i++;
  } else {
      do something else
      i++;
  }
}

if(in_array($field['link'],$unique[])){

if(in_array($field['link'],$unique)){

if(in_array($field['link'],$unique[])){