2     a      2
        3     a      3
        4     a      5
        5     b      1
        6     b      2
        7     b      4
        8     b      1
        9     b      5
        >>> for method in ['average', 'min', 'max', 'dense', 'first']:
        ...     df[f'{method}_rank'] = df.groupby('group')['value'].rank(method)
        >>> df
          group  value  average_rank  min_rank  max_rank  dense_rank  first_rank
        0     a      2           1.5       1.0       2.0         1.0         1.0
        1     a      4           4.0       4.0       4.0         3.0         4.0
        2     a      2           1.5       1.0       2.0         1.0         2.0
        3     a      3           3.0       3.0       3.0         2.0         3.0
        4     a      5           5.0       5.0       5.0         4.0         5.0
        5     b      1           1.5       1.0       2.0         1.0         1.0
        6     b      2           3.0       3.0       3.0         2.0         3.0
        7     b      4           4.0       4.0       4.0         3.0         4.0
        8     b      1           1.5       1.0       2.0         1.0         2.0
        9     b      5           5.0       5.0       5.0         4.0         5.0
        >