docs: def _game_keys_as_array(ds):
      """Turn keys of a Bigtable dataset into an array.
  
      Take g_GGG_m_MMM and create GGG.MMM numbers.
  
      Valuable when visualizing the distribution of a given dataset in
      the game keyspace.
      """
      ds = ds.map(lambda row_key, cell: row_key)
      # want 'g_0000001234_m_133' is '0000001234.133' and so forth
      ds = ds.map(lambda x:
                  tf.strings.to_number(tf.strings.substr(x, 2, 10) +
                                       '.' +
                                       tf.strings.substr(x, 15, 3),
                                       out_type=tf.float64))
      return make_single_array(ds)