@Substitution(name='<STR_LIT>')<EOL><INDENT>def ngroup(self, ascending=True):<DEDENT>
with _group_selection_context(self):<EOL><INDENT>index = self._selected_obj.index<EOL>result = Series(self.grouper.group_info[<NUM_LIT:0>], index)<EOL>if not ascending:<EOL><INDENT>result = self.ngroups - <NUM_LIT:1> - result<EOL><DEDENT>return result<EOL><DEDENT>
Number each group from 0 to the number of groups - 1.

This is the enumerative complement of cumcount.  Note that the
numbers given to the groups match the order in which the groups
would be seen when iterating over the groupby object, not the
order they are first observed.

.. versionadded:: 0.20.2

Parameters
----------
ascending : bool, default True
    If False, number in reverse, from number of group - 1 to 0.

See Also
--------
.cumcount : Number the rows in each group.

Examples
--------

>>> df = pd.DataFrame({"A": list("aaabba")})
>>> df
   A
0  a
1  a
2  a
3  b
4  b
5  a
>>> df.groupby('A').ngroup()
0    0
1    0
2    0
3    1
4    1
5    0
dtype: int64
>>> df.groupby('A').ngroup(ascending=False)
0    1
1    1
2    1
3    0
4    0
5    1
dtype: int64
>>> df.groupby(["A", [1,1,2,3,2,1]]).ngroup()
0    0
1    0
2    1
3    3
4    2
5    0
dtype: int64