Revert "Add levels property for MultiIndex (#973)"

This reverts commit 23dc764.

databricks/koalas/indexes.py

@@ -661,35 +661,6 @@ def __getattr__(self, item: str) -> Any:
     def rename(self, name, inplace=False):
         raise NotImplementedError()
 
-    @property
-    def levels(self) -> list:
-        """
-        Names of index columns in list.
-
-        .. note:: Be aware of the possibility of running into out
-            of memory issue if returned list is huge.
-
-        Examples
-        --------
-        >>> mi = pd.MultiIndex.from_arrays((list('abc'), list('def')))
-        >>> mi.names = ['level_1', 'level_2']
-        >>> kdf = ks.DataFrame({'a': [1, 2, 3]}, index=mi)
-        >>> kdf.index.levels
-        [['a', 'b', 'c'], ['d', 'e', 'f']]
-
-        >>> mi = pd.MultiIndex.from_arrays((list('bac'), list('fee')))
-        >>> mi.names = ['level_1', 'level_2']
-        >>> kdf = ks.DataFrame({'a': [1, 2, 3]}, index=mi)
-        >>> kdf.index.levels
-        [['a', 'b', 'c'], ['e', 'f']]
-        """
-        scols = self._kdf._internal.index_scols
-        row = self._kdf._sdf.select([F.collect_set(scol) for scol in scols]).first()
-
-        # use sorting is because pandas doesn't care the appearance order of level
-        # names, so e.g. if ['b', 'd', 'a'] will return as ['a', 'b', 'd']
-        return [sorted(col) for col in row]
-
     def __repr__(self):
         max_display_count = get_option("display.max_rows")
         if max_display_count is None:

databricks/koalas/missing/indexes.py

@@ -128,6 +128,7 @@ class _MissingPandasLikeMultiIndex(object):
     T = unsupported_property('T')
     codes = unsupported_property('codes')
     is_all_dates = unsupported_property('is_all_dates')
+    levels = unsupported_property('levels')
     levshape = unsupported_property('levshape')
     shape = unsupported_property('shape')
 

databricks/koalas/tests/test_indexes.py

@@ -300,15 +300,3 @@ def test_multiindex_from_arrays(self):
         kidx = ks.MultiIndex.from_arrays(arrays)
 
         self.assert_eq(pidx, kidx)
-
-    def test_multiindex_levels(self):
-        tuples = [[list('abc'), list('def')], [list('aac'), list('fed')]]
-
-        for tup in tuples:
-            pdf = pd.DataFrame({'a': [1, 2, 3]}, index=tup)
-            kdf = ks.from_pandas(pdf)
-
-            # pandas returns FronzeList, so need to convert it to normal list
-            # for comparison
-            pdf_levels = [list(i) for i in pdf.index.levels]
-            self.assertEqual(pdf_levels, kdf.index.levels)

docs/source/reference/indexing.rst

@@ -85,7 +85,6 @@ MultiIndex Properties
 
    MultiIndex.names
    MultiIndex.ndim
-   MultiIndex.levels
 
 MultiIndex Modifying and computations
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~