PERF: Allow jitting of groupby agg loop

doc/source/whatsnew/v1.2.0.rst

@@ -154,7 +154,7 @@ Deprecations
 Performance improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
--
+- Performance improvement in :meth:`GroupBy.agg` with the ``numba`` engine (:issue:`35759`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/core/groupby/generic.py

@@ -69,19 +69,16 @@
     GroupBy,
     _agg_template,
     _apply_docs,
+    _group_selection_context,
     _transform_template,
     get_groupby,
 )
+from pandas.core.groupby.numba_ import generate_numba_func, split_for_numba
 from pandas.core.indexes.api import Index, MultiIndex, all_indexes_same
 import pandas.core.indexes.base as ibase
 from pandas.core.internals import BlockManager, make_block
 from pandas.core.series import Series
-from pandas.core.util.numba_ import (
-    NUMBA_FUNC_CACHE,
-    generate_numba_func,
-    maybe_use_numba,
-    split_for_numba,
-)
+from pandas.core.util.numba_ import NUMBA_FUNC_CACHE, maybe_use_numba
 
 from pandas.plotting import boxplot_frame_groupby
 
@@ -229,6 +226,18 @@ def apply(self, func, *args, **kwargs):
     )
     def aggregate(self, func=None, *args, engine=None, engine_kwargs=None, **kwargs):
 
+        if maybe_use_numba(engine):
+            if not callable(func):
+                raise NotImplementedError(
+                    "Numba engine can only be used with a single function."
+                )
+            with _group_selection_context(self):
+                data = self._selected_obj
+            result, index = self._aggregate_with_numba(
+                data.to_frame(), func, *args, engine_kwargs=engine_kwargs, **kwargs
+            )
+            return self.obj._constructor(result.ravel(), index=index, name=data.name)
+
         relabeling = func is None
         columns = None
         if relabeling:
@@ -251,16 +260,11 @@ def aggregate(self, func=None, *args, engine=None, engine_kwargs=None, **kwargs)
                 return getattr(self, cyfunc)()
 
             if self.grouper.nkeys > 1:
-                return self._python_agg_general(
-                    func, *args, engine=engine, engine_kwargs=engine_kwargs, **kwargs
-                )
+                return self._python_agg_general(func, *args, **kwargs)
 
             try:
-                return self._python_agg_general(
-                    func, *args, engine=engine, engine_kwargs=engine_kwargs, **kwargs
-                )
+                return self._python_agg_general(func, *args, **kwargs)
             except (ValueError, KeyError):
-                # Do not catch Numba errors here, we want to raise and not fall back.
                 # TODO: KeyError is raised in _python_agg_general,
                 #  see see test_groupby.test_basic
                 result = self._aggregate_named(func, *args, **kwargs)
@@ -936,12 +940,19 @@ class DataFrameGroupBy(GroupBy[DataFrame]):
     )
     def aggregate(self, func=None, *args, engine=None, engine_kwargs=None, **kwargs):
 
-        relabeling, func, columns, order = reconstruct_func(func, **kwargs)
-
         if maybe_use_numba(engine):
-            return self._python_agg_general(
-                func, *args, engine=engine, engine_kwargs=engine_kwargs, **kwargs
+            if not callable(func):
+                raise NotImplementedError(
+                    "Numba engine can only be used with a single function."
+                )
+            with _group_selection_context(self):
+                data = self._selected_obj
+            result, index = self._aggregate_with_numba(
+                data, func, *args, engine_kwargs=engine_kwargs, **kwargs
             )
+            return self.obj._constructor(result, index=index, columns=data.columns)
+
+        relabeling, func, columns, order = reconstruct_func(func, **kwargs)
 
         result, how = self._aggregate(func, *args, **kwargs)
         if how is None:

pandas/core/groupby/groupby.py

@@ -34,7 +34,7 @@ class providing the base-class of operations.
 
 from pandas._config.config import option_context
 
-from pandas._libs import Timestamp
+from pandas._libs import Timestamp, lib
 import pandas._libs.groupby as libgroupby
 from pandas._typing import F, FrameOrSeries, FrameOrSeriesUnion, Scalar
 from pandas.compat.numpy import function as nv
@@ -61,11 +61,11 @@ class providing the base-class of operations.
 import pandas.core.common as com
 from pandas.core.frame import DataFrame
 from pandas.core.generic import NDFrame
-from pandas.core.groupby import base, ops
+from pandas.core.groupby import base, numba_, ops
 from pandas.core.indexes.api import CategoricalIndex, Index, MultiIndex
 from pandas.core.series import Series
 from pandas.core.sorting import get_group_index_sorter
-from pandas.core.util.numba_ import maybe_use_numba
+from pandas.core.util.numba_ import NUMBA_FUNC_CACHE
 
 _common_see_also = """
         See Also
@@ -384,7 +384,8 @@ class providing the base-class of operations.
     - dict of axis labels -> functions, function names or list of such.
 
     Can also accept a Numba JIT function with
-    ``engine='numba'`` specified.
+    ``engine='numba'`` specified. Only passing a single function is supported
+    with this engine.
 
     If the ``'numba'`` engine is chosen, the function must be
     a user defined function with ``values`` and ``index`` as the
@@ -1053,12 +1054,43 @@ def _cython_agg_general(
 
         return self._wrap_aggregated_output(output, index=self.grouper.result_index)
 
-    def _python_agg_general(
-        self, func, *args, engine="cython", engine_kwargs=None, **kwargs
-    ):
+    def _aggregate_with_numba(self, data, func, *args, engine_kwargs=None, **kwargs):
+        """
+        Perform groupby aggregation routine with the numba engine.
+
+        This routine mimics the data splitting routine of the DataSplitter class
+        to generate the indices of each group in the sorted data and then passes the
+        data and indices into a Numba jitted function.
+        """
+        group_keys = self.grouper._get_group_keys()
+        labels, _, n_groups = self.grouper.group_info
+        sorted_index = get_group_index_sorter(labels, n_groups)
+        sorted_labels = algorithms.take_nd(labels, sorted_index, allow_fill=False)
+        sorted_data = data.take(sorted_index, axis=self.axis).to_numpy()
+        starts, ends = lib.generate_slices(sorted_labels, n_groups)
+        cache_key = (func, "groupby_agg")
+        if cache_key in NUMBA_FUNC_CACHE:
+            # Return an already compiled version of roll_apply if available
+            numba_agg_func = NUMBA_FUNC_CACHE[cache_key]
+        else:
+            numba_agg_func = numba_.generate_numba_agg_func(
+                tuple(args), kwargs, func, engine_kwargs
+            )
+        result = numba_agg_func(
+            sorted_data, sorted_index, starts, ends, len(group_keys), len(data.columns),
+        )
+        if cache_key not in NUMBA_FUNC_CACHE:
+            NUMBA_FUNC_CACHE[cache_key] = numba_agg_func
+
+        if self.grouper.nkeys > 1:
+            index = MultiIndex.from_tuples(group_keys, names=self.grouper.names)
+        else:
+            index = Index(group_keys, name=self.grouper.names[0])
+        return result, index
+
+    def _python_agg_general(self, func, *args, **kwargs):
         func = self._is_builtin_func(func)
-        if engine != "numba":
-            f = lambda x: func(x, *args, **kwargs)
+        f = lambda x: func(x, *args, **kwargs)
 
         # iterate through "columns" ex exclusions to populate output dict
         output: Dict[base.OutputKey, np.ndarray] = {}
@@ -1069,21 +1101,11 @@ def _python_agg_general(
                 # agg_series below assumes ngroups > 0
                 continue
 
-            if maybe_use_numba(engine):
-                result, counts = self.grouper.agg_series(
-                    obj,
-                    func,
-                    *args,
-                    engine=engine,
-                    engine_kwargs=engine_kwargs,
-                    **kwargs,
-                )
-            else:
-                try:
-                    # if this function is invalid for this dtype, we will ignore it.
-                    result, counts = self.grouper.agg_series(obj, f)
-                except TypeError:
-                    continue
+            try:
+                # if this function is invalid for this dtype, we will ignore it.
+                result, counts = self.grouper.agg_series(obj, f)
+            except TypeError:
+                continue
 
             assert result is not None
             key = base.OutputKey(label=name, position=idx)

pandas/core/groupby/numba_.py

@@ -0,0 +1,172 @@
+"""Common utilities for Numba operations with groupby ops"""
+import inspect
+from typing import Any, Callable, Dict, Optional, Tuple
+
+import numpy as np
+
+from pandas._typing import FrameOrSeries, Scalar
+from pandas.compat._optional import import_optional_dependency
+
+from pandas.core.util.numba_ import (
+    NUMBA_FUNC_CACHE,
+    NumbaUtilError,
+    check_kwargs_and_nopython,
+    get_jit_arguments,
+    jit_user_function,
+)
+
+
+def split_for_numba(arg: FrameOrSeries) -> Tuple[np.ndarray, np.ndarray]:
+    """
+    Split pandas object into its components as numpy arrays for numba functions.
+
+    Parameters
+    ----------
+    arg : Series or DataFrame
+
+    Returns
+    -------
+    (ndarray, ndarray)
+        values, index
+    """
+    return arg.to_numpy(), arg.index.to_numpy()
+
+
+def validate_udf(func: Callable) -> None:
+    """
+    Validate user defined function for ops when using Numba with groupby ops.
+
+    The first signature arguments should include:
+
+    def f(values, index, ...):
+        ...
+
+    Parameters
+    ----------
+    func : function, default False
+        user defined function
+
+    Returns
+    -------
+    None
+
+    Raises
+    ------
+    NumbaUtilError
+    """
+    udf_signature = list(inspect.signature(func).parameters.keys())
+    expected_args = ["values", "index"]
+    min_number_args = len(expected_args)
+    if (
+        len(udf_signature) < min_number_args
+        or udf_signature[:min_number_args] != expected_args
+    ):
+        raise NumbaUtilError(
+            f"The first {min_number_args} arguments to {func.__name__} must be "
+            f"{expected_args}"
+        )
+
+
+def generate_numba_func(
+    func: Callable,
+    engine_kwargs: Optional[Dict[str, bool]],
+    kwargs: dict,
+    cache_key_str: str,
+) -> Tuple[Callable, Tuple[Callable, str]]:
+    """
+    Return a JITed function and cache key for the NUMBA_FUNC_CACHE
+
+    This _may_ be specific to groupby (as it's only used there currently).
+
+    Parameters
+    ----------
+    func : function
+        user defined function
+    engine_kwargs : dict or None
+        numba.jit arguments
+    kwargs : dict
+        kwargs for func
+    cache_key_str : str
+        string representing the second part of the cache key tuple
+
+    Returns
+    -------
+    (JITed function, cache key)
+
+    Raises
+    ------
+    NumbaUtilError
+    """
+    nopython, nogil, parallel = get_jit_arguments(engine_kwargs)
+    check_kwargs_and_nopython(kwargs, nopython)
+    validate_udf(func)
+    cache_key = (func, cache_key_str)
+    numba_func = NUMBA_FUNC_CACHE.get(
+        cache_key, jit_user_function(func, nopython, nogil, parallel)
+    )
+    return numba_func, cache_key
+
+
+def generate_numba_agg_func(
+    args: Tuple,
+    kwargs: Dict[str, Any],
+    func: Callable[..., Scalar],
+    engine_kwargs: Optional[Dict[str, bool]],
+) -> Callable[[np.ndarray, np.ndarray, np.ndarray, np.ndarray, int, int], np.ndarray]:
+    """
+    Generate a numba jitted agg function specified by values from engine_kwargs.
+
+    1. jit the user's function
+    2. Return a groupby agg function with the jitted function inline
+
+    Configurations specified in engine_kwargs apply to both the user's
+    function _AND_ the rolling apply function.
+
+    Parameters
+    ----------
+    args : tuple
+        *args to be passed into the function
+    kwargs : dict
+        **kwargs to be passed into the function
+    func : function
+        function to be applied to each window and will be JITed
+    engine_kwargs : dict
+        dictionary of arguments to be passed into numba.jit
+
+    Returns
+    -------
+    Numba function
+    """
+    nopython, nogil, parallel = get_jit_arguments(engine_kwargs)
+
+    check_kwargs_and_nopython(kwargs, nopython)
+
+    validate_udf(func)
+
+    numba_func = jit_user_function(func, nopython, nogil, parallel)
+
+    numba = import_optional_dependency("numba")
+
+    if parallel:
+        loop_range = numba.prange
+    else:
+        loop_range = range
+
+    @numba.jit(nopython=nopython, nogil=nogil, parallel=parallel)
+    def group_apply(
+        values: np.ndarray,
+        index: np.ndarray,
+        begin: np.ndarray,
+        end: np.ndarray,
+        num_groups: int,
+        num_columns: int,
+    ) -> np.ndarray:
+        result = np.empty((num_groups, num_columns))
+        for i in loop_range(num_groups):
+            group_index = index[begin[i] : end[i]]
+            for j in loop_range(num_columns):
+                group = values[begin[i] : end[i], j]
+                result[i, j] = numba_func(group, group_index, *args)
+        return result
+
+    return group_apply