BUG: Fixes to FixedForwardWindowIndexer and GroupbyIndexer (#43267)

doc/source/whatsnew/v1.3.4.rst

@@ -33,6 +33,7 @@ Fixed regressions
 
 Bug fixes
 ~~~~~~~~~
+- Bug in :meth:`pandas.DataFrame.groupby.rolling` and :class:`pandas.api.indexers.FixedForwardWindowIndexer` leading to segfaults and window endpoints being mixed across groups (:issue:`43267`)
 - Fixed bug in :meth:`.GroupBy.mean` with datetimelike values including ``NaT`` values returning incorrect results (:issue:`43132`)
 - Fixed bug in :meth:`Series.aggregate` not passing the first ``args`` to the user supplied ``func`` in certain cases (:issue:`43357`)
 

pandas/core/indexers/objects.py

@@ -266,9 +266,8 @@ def get_window_bounds(
             )
 
         start = np.arange(num_values, dtype="int64")
-        end_s = start[: -self.window_size] + self.window_size
-        end_e = np.full(self.window_size, num_values, dtype="int64")
-        end = np.concatenate([end_s, end_e])
+        end = start + self.window_size
+        end[end > num_values] = num_values
 
         return start, end
 
@@ -279,8 +278,8 @@ class GroupbyIndexer(BaseIndexer):
     def __init__(
         self,
         index_array: np.ndarray | None = None,
-        window_size: int = 0,
-        groupby_indicies: dict | None = None,
+        window_size: int | type[BaseIndexer] = 0,
+        groupby_indices: dict | None = None,
         window_indexer: type[BaseIndexer] = BaseIndexer,
         indexer_kwargs: dict | None = None,
         **kwargs,
@@ -292,9 +291,9 @@ def __init__(
             np.ndarray of the index of the original object that we are performing
             a chained groupby operation over. This index has been pre-sorted relative to
             the groups
-        window_size : int
+        window_size : int or BaseIndexer
             window size during the windowing operation
-        groupby_indicies : dict or None
+        groupby_indices : dict or None
             dict of {group label: [positional index of rows belonging to the group]}
         window_indexer : BaseIndexer
             BaseIndexer class determining the start and end bounds of each group
@@ -303,11 +302,13 @@ def __init__(
         **kwargs :
             keyword arguments that will be available when get_window_bounds is called
         """
-        self.groupby_indicies = groupby_indicies or {}
+        self.groupby_indices = groupby_indices or {}
         self.window_indexer = window_indexer
-        self.indexer_kwargs = indexer_kwargs or {}
+        self.indexer_kwargs = indexer_kwargs.copy() if indexer_kwargs else {}
         super().__init__(
-            index_array, self.indexer_kwargs.pop("window_size", window_size), **kwargs
+            index_array=index_array,
+            window_size=self.indexer_kwargs.pop("window_size", window_size),
+            **kwargs,
         )
 
     @Appender(get_window_bounds_doc)
@@ -323,8 +324,8 @@ def get_window_bounds(
         # 3) Append the window bounds in group order
         start_arrays = []
         end_arrays = []
-        window_indicies_start = 0
-        for key, indices in self.groupby_indicies.items():
+        window_indices_start = 0
+        for key, indices in self.groupby_indices.items():
             index_array: np.ndarray | None
 
             if self.index_array is not None:
@@ -341,18 +342,21 @@ def get_window_bounds(
             )
             start = start.astype(np.int64)
             end = end.astype(np.int64)
-            # Cannot use groupby_indicies as they might not be monotonic with the object
+            assert len(start) == len(
+                end
+            ), "these should be equal in length from get_window_bounds"
+            # Cannot use groupby_indices as they might not be monotonic with the object
             # we're rolling over
-            window_indicies = np.arange(
-                window_indicies_start, window_indicies_start + len(indices)
+            window_indices = np.arange(
+                window_indices_start, window_indices_start + len(indices)
             )
-            window_indicies_start += len(indices)
+            window_indices_start += len(indices)
             # Extend as we'll be slicing window like [start, end)
-            window_indicies = np.append(
-                window_indicies, [window_indicies[-1] + 1]
-            ).astype(np.int64)
-            start_arrays.append(window_indicies.take(ensure_platform_int(start)))
-            end_arrays.append(window_indicies.take(ensure_platform_int(end)))
+            window_indices = np.append(window_indices, [window_indices[-1] + 1]).astype(
+                np.int64, copy=False
+            )
+            start_arrays.append(window_indices.take(ensure_platform_int(start)))
+            end_arrays.append(window_indices.take(ensure_platform_int(end)))
         start = np.concatenate(start_arrays)
         end = np.concatenate(end_arrays)
         return start, end

pandas/core/window/ewm.py

@@ -798,7 +798,7 @@ def _get_window_indexer(self) -> GroupbyIndexer:
         GroupbyIndexer
         """
         window_indexer = GroupbyIndexer(
-            groupby_indicies=self._grouper.indices,
+            groupby_indices=self._grouper.indices,
             window_indexer=ExponentialMovingWindowIndexer,
         )
         return window_indexer

pandas/core/window/expanding.py

@@ -760,7 +760,7 @@ def _get_window_indexer(self) -> GroupbyIndexer:
         GroupbyIndexer
         """
         window_indexer = GroupbyIndexer(
-            groupby_indicies=self._grouper.indices,
+            groupby_indices=self._grouper.indices,
             window_indexer=ExpandingIndexer,
         )
         return window_indexer

pandas/core/window/rolling.py

@@ -311,8 +311,10 @@ def __iter__(self):
             center=self.center,
             closed=self.closed,
         )
-        # From get_window_bounds, those two should be equal in length of array
-        assert len(start) == len(end)
+
+        assert len(start) == len(
+            end
+        ), "these should be equal in length from get_window_bounds"
 
         for s, e in zip(start, end):
             result = obj.iloc[slice(s, e)]
@@ -563,6 +565,10 @@ def calc(x):
                     center=self.center,
                     closed=self.closed,
                 )
+                assert len(start) == len(
+                    end
+                ), "these should be equal in length from get_window_bounds"
+
                 return func(x, start, end, min_periods, *numba_args)
 
             with np.errstate(all="ignore"):
@@ -1501,6 +1507,11 @@ def cov_func(x, y):
                 center=self.center,
                 closed=self.closed,
             )
+
+            assert len(start) == len(
+                end
+            ), "these should be equal in length from get_window_bounds"
+
             with np.errstate(all="ignore"):
                 mean_x_y = window_aggregations.roll_mean(
                     x_array * y_array, start, end, min_periods
@@ -1540,6 +1551,11 @@ def corr_func(x, y):
                 center=self.center,
                 closed=self.closed,
             )
+
+            assert len(start) == len(
+                end
+            ), "these should be equal in length from get_window_bounds"
+
             with np.errstate(all="ignore"):
                 mean_x_y = window_aggregations.roll_mean(
                     x_array * y_array, start, end, min_periods
@@ -2490,11 +2506,11 @@ def _get_window_indexer(self) -> GroupbyIndexer:
         index_array = self._index_array
         if isinstance(self.window, BaseIndexer):
             rolling_indexer = type(self.window)
-            indexer_kwargs = self.window.__dict__
+            indexer_kwargs = self.window.__dict__.copy()
             assert isinstance(indexer_kwargs, dict)  # for mypy
             # We'll be using the index of each group later
             indexer_kwargs.pop("index_array", None)
-            window = 0
+            window = self.window
         elif self._win_freq_i8 is not None:
             rolling_indexer = VariableWindowIndexer
             window = self._win_freq_i8
@@ -2503,8 +2519,8 @@ def _get_window_indexer(self) -> GroupbyIndexer:
             window = self.window
         window_indexer = GroupbyIndexer(
             index_array=index_array,
-            window_size=window,
-            groupby_indicies=self._grouper.indices,
+            window_size=window,  # type: ignore[arg-type]
+            groupby_indices=self._grouper.indices,
             window_indexer=rolling_indexer,
             indexer_kwargs=indexer_kwargs,
         )

pandas/tests/groupby/test_missing.py

@@ -146,7 +146,7 @@ def test_min_count(func, min_count, value):
     tm.assert_frame_equal(result, expected)
 
 
-def test_indicies_with_missing():
+def test_indices_with_missing():
     # GH 9304
     df = DataFrame({"a": [1, 1, np.nan], "b": [2, 3, 4], "c": [5, 6, 7]})
     g = df.groupby(["a", "b"])

pandas/tests/window/test_base_indexer.py

@@ -3,7 +3,9 @@
 
 from pandas import (
     DataFrame,
+    MultiIndex,
     Series,
+    concat,
     date_range,
 )
 import pandas._testing as tm
@@ -13,6 +15,7 @@
 )
 from pandas.core.indexers.objects import (
     ExpandingIndexer,
+    FixedWindowIndexer,
     VariableOffsetWindowIndexer,
 )
 
@@ -293,3 +296,159 @@ def get_window_bounds(self, num_values, min_periods, center, closed):
     result = getattr(df.rolling(indexer), func)(*args)
     expected = DataFrame({"values": values})
     tm.assert_frame_equal(result, expected)
+
+
+@pytest.mark.parametrize(
+    "indexer_class", [FixedWindowIndexer, FixedForwardWindowIndexer, ExpandingIndexer]
+)
+@pytest.mark.parametrize("window_size", [1, 2, 12])
+@pytest.mark.parametrize(
+    "df_data",
+    [
+        {"a": [1, 1], "b": [0, 1]},
+        {"a": [1, 2], "b": [0, 1]},
+        {"a": [1] * 16, "b": [np.nan, 1, 2, np.nan] + list(range(4, 16))},
+    ],
+)
+def test_indexers_are_reusable_after_groupby_rolling(
+    indexer_class, window_size, df_data
+):
+    # GH 43267
+    df = DataFrame(df_data)
+    num_trials = 3
+    indexer = indexer_class(window_size=window_size)
+    original_window_size = indexer.window_size
+    for i in range(num_trials):
+        df.groupby("a")["b"].rolling(window=indexer, min_periods=1).mean()
+        assert indexer.window_size == original_window_size
+
+
+@pytest.mark.parametrize(
+    "window_size, num_values, expected_start, expected_end",
+    [
+        (1, 1, [0], [1]),
+        (1, 2, [0, 1], [1, 2]),
+        (2, 1, [0], [1]),
+        (2, 2, [0, 1], [2, 2]),
+        (5, 12, range(12), list(range(5, 12)) + [12] * 5),
+        (12, 5, range(5), [5] * 5),
+        (0, 0, np.array([]), np.array([])),
+        (1, 0, np.array([]), np.array([])),
+        (0, 1, [0], [0]),
+    ],
+)
+def test_fixed_forward_indexer_bounds(
+    window_size, num_values, expected_start, expected_end
+):
+    # GH 43267
+    indexer = FixedForwardWindowIndexer(window_size=window_size)
+    start, end = indexer.get_window_bounds(num_values=num_values)
+
+    tm.assert_numpy_array_equal(start, np.array(expected_start), check_dtype=False)
+    tm.assert_numpy_array_equal(end, np.array(expected_end), check_dtype=False)
+    assert len(start) == len(end)
+
+
+@pytest.mark.parametrize(
+    "df, window_size, expected",
+    [
+        (
+            DataFrame({"b": [0, 1, 2], "a": [1, 2, 2]}),
+            2,
+            Series(
+                [0, 1.5, 2.0],
+                index=MultiIndex.from_arrays([[1, 2, 2], range(3)], names=["a", None]),
+                name="b",
+                dtype=np.float64,
+            ),
+        ),
+        (
+            DataFrame(
+                {
+                    "b": [np.nan, 1, 2, np.nan] + list(range(4, 18)),
+                    "a": [1] * 7 + [2] * 11,
+                    "c": range(18),
+                }
+            ),
+            12,
+            Series(
+                [
+                    3.6,
+                    3.6,
+                    4.25,
+                    5.0,
+                    5.0,
+                    5.5,
+                    6.0,
+                    12.0,
+                    12.5,
+                    13.0,
+                    13.5,
+                    14.0,
+                    14.5,
+                    15.0,
+                    15.5,
+                    16.0,
+                    16.5,
+                    17.0,
+                ],
+                index=MultiIndex.from_arrays(
+                    [[1] * 7 + [2] * 11, range(18)], names=["a", None]
+                ),
+                name="b",
+                dtype=np.float64,
+            ),
+        ),
+    ],
+)
+def test_rolling_groupby_with_fixed_forward_specific(df, window_size, expected):
+    # GH 43267
+    indexer = FixedForwardWindowIndexer(window_size=window_size)
+    result = df.groupby("a")["b"].rolling(window=indexer, min_periods=1).mean()
+    tm.assert_series_equal(result, expected)
+
+
+@pytest.mark.parametrize(
+    "group_keys",
+    [
+        (1,),
+        (1, 2),
+        (2, 1),
+        (1, 1, 2),
+        (1, 2, 1),
+        (1, 1, 2, 2),
+        (1, 2, 3, 2, 3),
+        (1, 1, 2) * 4,
+        (1, 2, 3) * 5,
+    ],
+)
+@pytest.mark.parametrize("window_size", [1, 2, 3, 4, 5, 8, 20])
+def test_rolling_groupby_with_fixed_forward_many(group_keys, window_size):
+    # GH 43267
+    df = DataFrame(
+        {
+            "a": np.array(list(group_keys)),
+            "b": np.arange(len(group_keys), dtype=np.float64) + 17,
+            "c": np.arange(len(group_keys), dtype=np.int64),
+        }
+    )
+
+    indexer = FixedForwardWindowIndexer(window_size=window_size)
+    result = df.groupby("a")["b"].rolling(window=indexer, min_periods=1).sum()
+    result.index.names = ["a", "c"]
+
+    groups = df.groupby("a")[["a", "b"]]
+    manual = concat(
+        [
+            g.assign(
+                b=[
+                    g["b"].iloc[i : i + window_size].sum(min_count=1)
+                    for i in range(len(g))
+                ]
+            )
+            for _, g in groups
+        ]
+    )
+    manual = manual.set_index(["a", "c"])["b"]
+
+    tm.assert_series_equal(result, manual)