fix: make explode respect the index labels (#1064)

Author: shobsi

bigframes/core/blocks.py

@@ -1390,7 +1390,7 @@ def explode(
                 expr,
                 column_labels=self.column_labels,
                 index_columns=self.index_columns,
-                index_labels=self.column_labels.names,
+                index_labels=self._index_labels,
             )
 
     def _standard_stats(self, column_id) -> typing.Sequence[agg_ops.UnaryAggregateOp]:

tests/system/small/test_multiindex.py

@@ -1178,7 +1178,7 @@ def test_column_multi_index_dot_not_supported():
         bf1 @ bf2
 
 
-def test_explode_w_multi_index():
+def test_explode_w_column_multi_index():
     data = [[[1, 1], np.nan, [3, 3]], [[2], [5], []]]
     multi_level_columns = pandas.MultiIndex.from_arrays(
         [["col0", "col0", "col1"], ["col00", "col01", "col11"]]
@@ -1197,6 +1197,24 @@ def test_explode_w_multi_index():
     )
 
 
+def test_explode_w_multi_index():
+    data = [[[1, 1], np.nan, [3, 3]], [[2], [5], []]]
+    columns = ["col00", "col01", "col11"]
+    multi_index = pandas.MultiIndex.from_frame(
+        pandas.DataFrame({"idx0": [5, 1], "idx1": ["z", "x"]})
+    )
+
+    df = bpd.DataFrame(data, index=multi_index, columns=columns)
+    pd_df = df.to_pandas()
+
+    pandas.testing.assert_frame_equal(
+        df.explode("col00").to_pandas(),
+        pd_df.explode("col00"),
+        check_dtype=False,
+        check_index_type=False,
+    )
+
+
 def test_column_multi_index_w_na_stack(scalars_df_index, scalars_pandas_df_index):
     columns = ["int64_too", "int64_col", "rowindex_2"]
     level1 = pandas.Index(["b", "c", "d"])

tests/system/small/test_series.py

@@ -3852,6 +3852,28 @@ def test_series_explode(data):
         pytest.param([5, 1, 3, 2], False, id="ignore_unordered_index"),
         pytest.param(["z", "x", "a", "b"], True, id="str_index"),
         pytest.param(["z", "x", "a", "b"], False, id="ignore_str_index"),
+        pytest.param(
+            pd.Index(["z", "x", "a", "b"], name="idx"), True, id="str_named_index"
+        ),
+        pytest.param(
+            pd.Index(["z", "x", "a", "b"], name="idx"),
+            False,
+            id="ignore_str_named_index",
+        ),
+        pytest.param(
+            pd.MultiIndex.from_frame(
+                pd.DataFrame({"idx0": [5, 1, 3, 2], "idx1": ["z", "x", "a", "b"]})
+            ),
+            True,
+            id="multi_index",
+        ),
+        pytest.param(
+            pd.MultiIndex.from_frame(
+                pd.DataFrame({"idx0": [5, 1, 3, 2], "idx1": ["z", "x", "a", "b"]})
+            ),
+            False,
+            id="ignore_multi_index",
+        ),
     ],
 )
 def test_series_explode_w_index(index, ignore_index):