PERF: Improve performance in rolling.mean(engine="numba")

doc/source/whatsnew/v1.4.0.rst

@@ -357,7 +357,7 @@ Performance improvements
 - Performance improvement in :meth:`GroupBy.quantile` (:issue:`43469`)
 - :meth:`SparseArray.min` and :meth:`SparseArray.max` no longer require converting to a dense array (:issue:`43526`)
 - Performance improvement in :meth:`SparseArray.take` with ``allow_fill=False`` (:issue:`43654`)
--
+- Performance improvement in :meth:`.Rolling.mean` and :meth:`.Expanding.mean` with ``engine="numba"`` (:issue:`43612`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/_numba/executor.py

@@ -0,0 +1,59 @@
+from __future__ import annotations
+
+from typing import Callable
+
+import numpy as np
+
+from pandas._typing import Scalar
+from pandas.compat._optional import import_optional_dependency
+
+from pandas.core.util.numba_ import (
+    NUMBA_FUNC_CACHE,
+    get_jit_arguments,
+)
+
+
+def generate_shared_aggregator(
+    func: Callable[..., Scalar],
+    engine_kwargs: dict[str, bool] | None,
+    cache_key_str: str,
+):
+    """
+    Generate a Numba function that loops over the columns 2D object and applies
+    a 1D numba kernel over each column.
+
+    Parameters
+    ----------
+    func : function
+        aggregation function to be applied to each column
+    engine_kwargs : dict
+        dictionary of arguments to be passed into numba.jit
+    cache_key_str: str
+        string to access the compiled function of the form
+        <caller_type>_<aggregation_type> e.g. rolling_mean, groupby_mean
+
+    Returns
+    -------
+    Numba function
+    """
+    nopython, nogil, parallel = get_jit_arguments(engine_kwargs, None)
+
+    cache_key = (func, cache_key_str)
+    if cache_key in NUMBA_FUNC_CACHE:
+        return NUMBA_FUNC_CACHE[cache_key]
+
+    numba = import_optional_dependency("numba")
+
+    @numba.jit(nopython=nopython, nogil=nogil, parallel=parallel)
+    def column_looper(
+        values: np.ndarray,
+        start: np.ndarray,
+        end: np.ndarray,
+        min_periods: int,
+    ):
+        result = np.empty((len(start), values.shape[1]), dtype=np.float64)
+        for i in numba.prange(values.shape[1]):
+            result[:, i] = func(values[:, i], start, end, min_periods)
+        return result
+
+    return column_looper

pandas/core/_numba/kernels/__init__.py

@@ -0,0 +1,3 @@
+from pandas.core._numba.kernels.mean_ import sliding_mean
+
+__all__ = ["sliding_mean"]

pandas/core/_numba/kernels/mean_.py

@@ -0,0 +1,119 @@
+"""
+Numba 1D aggregation kernels that can be shared by
+* Dataframe / Series
+* groupby
+* rolling / expanding
+
+Mirrors pandas/_libs/window/aggregation.pyx
+"""
+from __future__ import annotations
+
+import numba
+import numpy as np
+
+
+@numba.jit(nopython=True, nogil=True, parallel=False)
+def is_monotonic_increasing(bounds: np.ndarray) -> bool:
+    """Check if int64 values are monotonically increasing."""
+    n = len(bounds)
+    if n < 2:
+        return True
+    prev = bounds[0]
+    for i in range(1, n):
+        cur = bounds[i]
+        if cur < prev:
+            return False
+        prev = cur
+    return True
+
+
+@numba.jit(nopython=True, nogil=True, parallel=False)
+def add_mean(
+    val: float, nobs: int, sum_x: float, neg_ct: int, compensation: float
+) -> tuple[int, float, int, float]:
+    if not np.isnan(val):
+        nobs += 1
+        y = val - compensation
+        t = sum_x + y
+        compensation = t - sum_x - y
+        sum_x = t
+        if val < 0:
+            neg_ct += 1
+    return nobs, sum_x, neg_ct, compensation
+
+
+@numba.jit(nopython=True, nogil=True, parallel=False)
+def remove_mean(
+    val: float, nobs: int, sum_x: float, neg_ct: int, compensation: float
+) -> tuple[int, float, int, float]:
+    if not np.isnan(val):
+        nobs -= 1
+        y = -val - compensation
+        t = sum_x + y
+        compensation = t - sum_x - y
+        sum_x = t
+        if val < 0:
+            neg_ct -= 1
+    return nobs, sum_x, neg_ct, compensation
+
+
+@numba.jit(nopython=True, nogil=True, parallel=False)
+def sliding_mean(
+    values: np.ndarray,
+    start: np.ndarray,
+    end: np.ndarray,
+    min_periods: int,
+) -> np.ndarray:
+    N = len(start)
+    nobs = 0
+    sum_x = 0.0
+    neg_ct = 0
+    compensation_add = 0.0
+    compensation_remove = 0.0
+
+    is_monotonic_increasing_bounds = is_monotonic_increasing(
+        start
+    ) and is_monotonic_increasing(end)
+
+    output = np.empty(N, dtype=np.float64)
+
+    for i in range(N):
+        s = start[i]
+        e = end[i]
+        if i == 0 or not is_monotonic_increasing_bounds:
+            for j in range(s, e):
+                val = values[j]
+                nobs, sum_x, neg_ct, compensation_add = add_mean(
+                    val, nobs, sum_x, neg_ct, compensation_add
+                )
+        else:
+            for j in range(start[i - 1], s):
+                val = values[j]
+                nobs, sum_x, neg_ct, compensation_remove = remove_mean(
+                    val, nobs, sum_x, neg_ct, compensation_remove
+                )
+
+            for j in range(end[i - 1], e):
+                val = values[j]
+                nobs, sum_x, neg_ct, compensation_add = add_mean(
+                    val, nobs, sum_x, neg_ct, compensation_add
+                )
+
+        if nobs >= min_periods and nobs > 0:
+            result = sum_x / nobs
+            if neg_ct == 0 and result < 0:
+                result = 0
+            elif neg_ct == nobs and result > 0:
+                result = 0
+        else:
+            result = np.nan
+
+        output[i] = result
+
+        if not is_monotonic_increasing_bounds:
+            nobs = 0
+            sum_x = 0.0
+            neg_ct = 0
+            compensation_remove = 0.0
+
+    return output

pandas/core/window/rolling.py

@@ -49,6 +49,7 @@
 )
 from pandas.core.dtypes.missing import notna
 
+from pandas.core._numba import executor
 from pandas.core.algorithms import factorize
 from pandas.core.apply import ResamplerWindowApply
 from pandas.core.arrays import ExtensionArray
@@ -576,6 +577,44 @@ def calc(x):
         else:
             return self._apply_tablewise(homogeneous_func, name)
 
+    def _numba_apply(
+        self,
+        func: Callable[..., Any],
+        numba_cache_key_str: str,
+        engine_kwargs: dict[str, bool] | None = None,
+    ):
+        window_indexer = self._get_window_indexer()
+        min_periods = (
+            self.min_periods
+            if self.min_periods is not None
+            else window_indexer.window_size
+        )
+        obj = self._create_data(self._selected_obj)
+        if self.axis == 1:
+            obj = obj.T
+        values = self._prep_values(obj.to_numpy())
+        if values.ndim == 1:
+            values = values.reshape(-1, 1)
+        start, end = window_indexer.get_window_bounds(
+            num_values=len(values),
+            min_periods=min_periods,
+            center=self.center,
+            closed=self.closed,
+        )
+        aggregator = executor.generate_shared_aggregator(
+            func, engine_kwargs, numba_cache_key_str
+        )
+        result = aggregator(values, start, end, min_periods)
+        NUMBA_FUNC_CACHE[(func, numba_cache_key_str)] = aggregator
+        result = result.T if self.axis == 1 else result
+        if obj.ndim == 1:
+            result = result.squeeze()
+            out = obj._constructor(result, index=obj.index, name=obj.name)
+            return out
+        else:
+            out = obj._constructor(result, index=obj.index, columns=obj.columns)
+            return self._resolve_output(out, obj)
+
     def aggregate(self, func, *args, **kwargs):
         result = ResamplerWindowApply(self, func, args=args, kwargs=kwargs).agg()
         if result is None:
@@ -1331,15 +1370,16 @@ def mean(
         if maybe_use_numba(engine):
             if self.method == "table":
                 func = generate_manual_numpy_nan_agg_with_axis(np.nanmean)
+                return self.apply(
+                    func,
+                    raw=True,
+                    engine=engine,
+                    engine_kwargs=engine_kwargs,
+                )
             else:
-                func = np.nanmean
+                from pandas.core._numba.kernels import sliding_mean
 
-            return self.apply(
-                func,
-                raw=True,
-                engine=engine,
-                engine_kwargs=engine_kwargs,
-            )
+                return self._numba_apply(sliding_mean, "rolling_mean", engine_kwargs)
         window_func = window_aggregations.roll_mean
         return self._apply(window_func, name="mean", **kwargs)
 

pandas/tests/window/test_numba.py

@@ -43,44 +43,52 @@ def f(x, *args):
         )
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "data", [DataFrame(np.eye(5)), Series(range(5), name="foo")]
+    )
     def test_numba_vs_cython_rolling_methods(
-        self, nogil, parallel, nopython, arithmetic_numba_supported_operators
+        self, data, nogil, parallel, nopython, arithmetic_numba_supported_operators
     ):
 
         method = arithmetic_numba_supported_operators
 
         engine_kwargs = {"nogil": nogil, "parallel": parallel, "nopython": nopython}
 
-        df = DataFrame(np.eye(5))
-        roll = df.rolling(2)
+        roll = data.rolling(2)
         result = getattr(roll, method)(engine="numba", engine_kwargs=engine_kwargs)
         expected = getattr(roll, method)(engine="cython")
 
         # Check the cache
-        assert (getattr(np, f"nan{method}"), "Rolling_apply_single") in NUMBA_FUNC_CACHE
+        if method != "mean":
+            assert (
+                getattr(np, f"nan{method}"),
+                "Rolling_apply_single",
+            ) in NUMBA_FUNC_CACHE
 
-        tm.assert_frame_equal(result, expected)
+        tm.assert_equal(result, expected)
 
+    @pytest.mark.parametrize("data", [DataFrame(np.eye(5)), Series(range(5))])
     def test_numba_vs_cython_expanding_methods(
-        self, nogil, parallel, nopython, arithmetic_numba_supported_operators
+        self, data, nogil, parallel, nopython, arithmetic_numba_supported_operators
     ):
 
         method = arithmetic_numba_supported_operators
 
         engine_kwargs = {"nogil": nogil, "parallel": parallel, "nopython": nopython}
 
-        df = DataFrame(np.eye(5))
-        expand = df.expanding()
+        data = DataFrame(np.eye(5))
+        expand = data.expanding()
         result = getattr(expand, method)(engine="numba", engine_kwargs=engine_kwargs)
         expected = getattr(expand, method)(engine="cython")
 
         # Check the cache
-        assert (
-            getattr(np, f"nan{method}"),
-            "Expanding_apply_single",
-        ) in NUMBA_FUNC_CACHE
+        if method != "mean":
+            assert (
+                getattr(np, f"nan{method}"),
+                "Expanding_apply_single",
+            ) in NUMBA_FUNC_CACHE
 
-        tm.assert_frame_equal(result, expected)
+        tm.assert_equal(result, expected)
 
     @pytest.mark.parametrize("jit", [True, False])
     def test_cache_apply(self, jit, nogil, parallel, nopython):