FIX-#7143: Constructing a DataFrame from a Modin Series with tuple na…

…me should produce MultiIndex columns (#7214)

Signed-off-by: Jonathan Shi <jhshi07@gmail.com>

modin/pandas/series.py

@@ -185,7 +185,11 @@ def _set_name(self, name: Hashable) -> None:
         """
         if name is None:
             name = MODIN_UNNAMED_SERIES_LABEL
-        self._query_compiler.columns = [name]
+        if isinstance(name, tuple):
+            columns = pandas.MultiIndex.from_tuples(tuples=[name])
+        else:
+            columns = [name]
+        self._query_compiler.columns = columns
 
     name: Hashable = property(_get_name, _set_name)
     _parent = None

modin/tests/pandas/dataframe/test_default.py

@@ -1485,3 +1485,13 @@ def test_setattr_axes():
 def test_attrs(data):
     modin_df, pandas_df = create_test_dfs(data)
     eval_general(modin_df, pandas_df, lambda df: df.attrs)
+
+
+def test_df_from_series_with_tuple_name():
+    # Tests that creating a DataFrame from a series with a tuple name results in
+    # a DataFrame with MultiIndex columns.
+    pandas_result = pandas.DataFrame(pandas.Series(name=("a", 1)))
+    # 1. Creating a Modin DF from native pandas Series
+    df_equals(pd.DataFrame(pandas.Series(name=("a", 1))), pandas_result)
+    # 2. Creating a Modin DF from Modin Series
+    df_equals(pd.DataFrame(pd.Series(name=("a", 1))), pandas_result)

modin/tests/pandas/test_series.py

@@ -2642,6 +2642,23 @@ def test_name(data):
     assert modin_series._query_compiler.columns == ["New_name"]
 
 
+def test_tuple_name():
+    names = [("a", 1), ("a", "b", "c"), "flat"]
+    s = pd.Series(name=names[0])
+    # The internal representation of the Series stores the name as a column label.
+    # When it is a tuple, this label is a MultiIndex object, and this test ensures that
+    # the Series's name property remains a tuple.
+    assert s.name == names[0]
+    assert isinstance(s.name, tuple)
+    # Setting the name to a tuple of a different level or a non-tuple should not error.
+    s.name = names[1]
+    assert s.name == names[1]
+    assert isinstance(s.name, tuple)
+    s.name = names[2]
+    assert s.name == names[2]
+    assert isinstance(s.name, str)
+
+
 @pytest.mark.parametrize("data", test_data_values, ids=test_data_keys)
 def test_nbytes(data):
     modin_series, pandas_series = create_test_series(data)