add unit tests for issue #19351 (#29438)

Author: Andy

pandas/tests/test_multilevel.py

@@ -358,6 +358,49 @@ def test_unstack(self):
         # test that int32 work
         self.ymd.astype(np.int32).unstack()
 
+    @pytest.mark.parametrize(
+        "result_rows,result_columns,index_product,expected_row",
+        [
+            (
+                [[1, 1, None, None, 30.0, None], [2, 2, None, None, 30.0, None]],
+                [u"ix1", u"ix2", u"col1", u"col2", u"col3", u"col4"],
+                2,
+                [None, None, 30.0, None],
+            ),
+            (
+                [[1, 1, None, None, 30.0], [2, 2, None, None, 30.0]],
+                [u"ix1", u"ix2", u"col1", u"col2", u"col3"],
+                2,
+                [None, None, 30.0],
+            ),
+            (
+                [[1, 1, None, None, 30.0], [2, None, None, None, 30.0]],
+                [u"ix1", u"ix2", u"col1", u"col2", u"col3"],
+                None,
+                [None, None, 30.0],
+            ),
+        ],
+    )
+    def test_unstack_partial(
+        self, result_rows, result_columns, index_product, expected_row
+    ):
+        # check for regressions on this issue:
+        # https://github.com/pandas-dev/pandas/issues/19351
+        # make sure DataFrame.unstack() works when its run on a subset of the DataFrame
+        # and the Index levels contain values that are not present in the subset
+        result = pd.DataFrame(result_rows, columns=result_columns).set_index(
+            [u"ix1", "ix2"]
+        )
+        result = result.iloc[1:2].unstack("ix2")
+        expected = pd.DataFrame(
+            [expected_row],
+            columns=pd.MultiIndex.from_product(
+                [result_columns[2:], [index_product]], names=[None, "ix2"]
+            ),
+            index=pd.Index([2], name="ix1"),
+        )
+        tm.assert_frame_equal(result, expected)
+
     def test_unstack_multiple_no_empty_columns(self):
         index = MultiIndex.from_tuples(
             [(0, "foo", 0), (0, "bar", 0), (1, "baz", 1), (1, "qux", 1)]