Series(data=df, index=None) seems to be incorrectly instantiated

Hi, I saw it is now possible to create a Series from a DataFrame without any additional index parameter. However, I can not print or sort_index a Series which has been created in this way. I guess the Series is incorrectly instantiated and probably other actions would fail too.

>>> df = ks.DataFrame({"a": [1, 2, 3, 4, 5]})
>>> ser = ks.Series(df)
>>> print(ser)
Traceback (most recent call last):
  File "D:\Dev\Utils\Miniconda\envs\koalas-dev\lib\site-packages\pandas\core\indexes\base.py", line 2646, in get_loc
    return self._engine.get_loc(key)
  File "pandas\_libs\index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc
  File "pandas\_libs\index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc
  File "pandas\_libs\hashtable_class_helper.pxi", line 1619, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas\_libs\hashtable_class_helper.pxi", line 1627, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: None

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "D:\Dev\koalas\databricks\koalas\series.py", line 5232, in __repr__
    pser = self._kdf._get_or_create_repr_pandas_cache(max_display_count)[self.name]
  File "D:\Dev\Utils\Miniconda\envs\koalas-dev\lib\site-packages\pandas\core\frame.py", line 2800, in __getitem__
    indexer = self.columns.get_loc(key)
  File "D:\Dev\Utils\Miniconda\envs\koalas-dev\lib\site-packages\pandas\core\indexes\base.py", line 2648, in get_loc
    return self._engine.get_loc(self._maybe_cast_indexer(key))
  File "pandas\_libs\index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc
  File "pandas\_libs\index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc
  File "pandas\_libs\hashtable_class_helper.pxi", line 1619, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas\_libs\hashtable_class_helper.pxi", line 1627, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: None

>>> ser.sort_index()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "D:\Dev\koalas\databricks\koalas\series.py", line 2227, in sort_index
    kdf = self._kdf[[self.name]].sort_index(
  File "D:\Dev\koalas\databricks\koalas\frame.py", line 10130, in __getitem__
    return self.loc[:, list(key)]
  File "D:\Dev\koalas\databricks\koalas\indexing.py", line 441, in __getitem__
    cols_sel
  File "D:\Dev\koalas\databricks\koalas\indexing.py", line 313, in _select_cols
    return self._select_cols_by_iterable(cols_sel, missing_keys)
  File "D:\Dev\koalas\databricks\koalas\indexing.py", line 1175, in _select_cols_by_iterable
    raise KeyError("['{}'] not in index".format(name_like_string(key)))
KeyError: "['__none__'] not in index"

[LucasG0]

Alright, pandas does not support it either. For internal purposes (#1737), I actually found the function first_series instead of passing DataFrame as Series constructor parameter.

[HyukjinKwon]

I’ll tentatively resolve this ticket since pandas doesn’t support either.