You can get all the values in a hash by calling `my_hash.values` rather than mapping.

```ruby
def all_units
  [:rows, :columns, :boxes].map do |message|
    send(message).values
  end.flatten
end
```

Now that we aren't passing  a block to each of the units, we could simplify the method even further:

```ruby
def all_units
  rows.values + columns.values + boxes.values
end
```