Remove split_out (#170)

flox/core.py

@@ -736,13 +736,6 @@ def _squeeze_results(results: IntermediateDict, axis: T_Axes) -> IntermediateDic
     return newresults
 
 
-def _split_groups(array, j, slicer):
-    """Slices out chunks when split_out > 1"""
-    results = {"groups": array["groups"][..., slicer]}
-    results["intermediates"] = [v[..., slicer] for v in array["intermediates"]]
-    return results
-
-
 def _finalize_results(
     results: IntermediateDict,
     agg: Aggregation,
@@ -997,38 +990,6 @@ def _grouped_combine(
     return results
 
 
-def split_blocks(applied, split_out, expected_groups, split_name):
-    import dask.array
-    from dask.array.core import normalize_chunks
-    from dask.highlevelgraph import HighLevelGraph
-
-    chunk_tuples = tuple(itertools.product(*tuple(range(n) for n in applied.numblocks)))
-    ngroups = len(expected_groups)
-    group_chunks = normalize_chunks(np.ceil(ngroups / split_out), (ngroups,))
-    idx = tuple(np.cumsum((0,) + group_chunks[0]))
-
-    # split each block into `split_out` chunks
-    dsk = {}
-    for i in chunk_tuples:
-        for j in range(split_out):
-            dsk[(split_name, *i, j)] = (
-                _split_groups,
-                (applied.name, *i),
-                j,
-                slice(idx[j], idx[j + 1]),
-            )
-
-    # now construct an array that can be passed to _tree_reduce
-    intergraph = HighLevelGraph.from_collections(split_name, dsk, dependencies=(applied,))
-    intermediate = dask.array.Array(
-        intergraph,
-        name=split_name,
-        chunks=applied.chunks + ((1,) * split_out,),
-        meta=applied._meta,
-    )
-    return intermediate, group_chunks
-
-
 def _reduce_blockwise(
     array,
     by,
@@ -1169,7 +1130,6 @@ def dask_groupby_agg(
     agg: Aggregation,
     expected_groups: pd.Index | None,
     axis: T_Axes = (),
-    split_out: int = 1,
     fill_value: Any = None,
     method: T_Method = "map-reduce",
     reindex: bool = False,
@@ -1186,19 +1146,14 @@ def dask_groupby_agg(
     assert isinstance(axis, Sequence)
     assert all(ax >= 0 for ax in axis)
 
-    if method == "blockwise" and (split_out > 1 or not isinstance(by, np.ndarray)):
-        raise NotImplementedError
-
-    if split_out > 1 and expected_groups is None:
-        # This could be implemented using the "hash_split" strategy
-        # from dask.dataframe
+    if method == "blockwise" and not isinstance(by, np.ndarray):
         raise NotImplementedError
 
     inds = tuple(range(array.ndim))
     name = f"groupby_{agg.name}"
-    token = dask.base.tokenize(array, by, agg, expected_groups, axis, split_out)
+    token = dask.base.tokenize(array, by, agg, expected_groups, axis)
 
-    if expected_groups is None and (reindex or split_out > 1):
+    if expected_groups is None and reindex:
         expected_groups = _get_expected_groups(by, sort=sort)
 
     by_input = by
@@ -1229,9 +1184,7 @@ def dask_groupby_agg(
     #       This allows us to discover groups at compute time, support argreductions, lower intermediate
     #       memory usage (but method="cohorts" would also work to reduce memory in some cases)
 
-    do_simple_combine = (
-        method != "blockwise" and reindex and not _is_arg_reduction(agg) and split_out == 1
-    )
+    do_simple_combine = method != "blockwise" and reindex and not _is_arg_reduction(agg)
     if method == "blockwise":
         #  use the "non dask" code path, but applied blockwise
         blockwise_method = partial(
@@ -1244,14 +1197,14 @@ def dask_groupby_agg(
             func=agg.chunk,
             fill_value=agg.fill_value["intermediate"],
             dtype=agg.dtype["intermediate"],
-            reindex=reindex or (split_out > 1),
+            reindex=reindex,
         )
         if do_simple_combine:
             # Add a dummy dimension that then gets reduced over
             blockwise_method = tlz.compose(_expand_dims, blockwise_method)
 
     # apply reduction on chunk
-    applied = dask.array.blockwise(
+    intermediate = dask.array.blockwise(
         partial(
             blockwise_method,
             axis=axis,
@@ -1271,18 +1224,14 @@ def dask_groupby_agg(
         token=f"{name}-chunk-{token}",
     )
 
-    if split_out > 1:
-        intermediate, group_chunks = split_blocks(
-            applied, split_out, expected_groups, split_name=f"{name}-split-{token}"
-        )
-    else:
-        intermediate = applied
-        if expected_groups is None:
-            if is_duck_dask_array(by_input):
-                expected_groups = None
-            else:
-                expected_groups = _get_expected_groups(by_input, sort=sort)
-        group_chunks = ((len(expected_groups),) if expected_groups is not None else (np.nan,),)
+    if expected_groups is None:
+        if is_duck_dask_array(by_input):
+            expected_groups = None
+        else:
+            expected_groups = _get_expected_groups(by_input, sort=sort)
+    group_chunks: tuple[tuple[Union[int, float], ...]] = (
+        (len(expected_groups),) if expected_groups is not None else (np.nan,),
+    )
 
     if method in ["map-reduce", "cohorts", "split-reduce"]:
         combine: Callable[..., IntermediateDict]
@@ -1311,9 +1260,7 @@ def dask_groupby_agg(
         if method == "map-reduce":
             reduced = tree_reduce(
                 intermediate,
-                aggregate=partial(
-                    aggregate, expected_groups=None if split_out > 1 else expected_groups
-                ),
+                aggregate=partial(aggregate, expected_groups=expected_groups),
             )
             if is_duck_dask_array(by_input) and expected_groups is None:
                 groups = _extract_unknown_groups(reduced, group_chunks=group_chunks, dtype=by.dtype)
@@ -1380,7 +1327,7 @@ def dask_groupby_agg(
         raise ValueError(f"Unknown method={method}.")
 
     # extract results from the dict
-    output_chunks = reduced.chunks[: -(len(axis) + int(split_out > 1))] + group_chunks
+    output_chunks = reduced.chunks[: -len(axis)] + group_chunks
     ochunks = tuple(range(len(chunks_v)) for chunks_v in output_chunks)
     layer2: dict[tuple, tuple] = {}
     agg_name = f"{name}-{token}"
@@ -1392,10 +1339,7 @@ def dask_groupby_agg(
                 nblocks = tuple(len(array.chunks[ax]) for ax in axis)
                 inchunk = ochunk[:-1] + np.unravel_index(ochunk[-1], nblocks)
         else:
-            inchunk = ochunk[:-1] + (0,) * (len(axis) - 1)
-            if split_out > 1:
-                inchunk = inchunk + (0,)
-            inchunk = inchunk + (ochunk[-1],)
+            inchunk = ochunk[:-1] + (0,) * (len(axis) - 1) + (ochunk[-1],)
 
         layer2[(agg_name, *ochunk)] = (operator.getitem, (reduced.name, *inchunk), agg.name)
 
@@ -1516,7 +1460,6 @@ def groupby_reduce(
     fill_value=None,
     dtype: np.typing.DTypeLike = None,
     min_count: int | None = None,
-    split_out: int = 1,
     method: T_Method = "map-reduce",
     engine: T_Engine = "numpy",
     reindex: bool | None = None,
@@ -1555,8 +1498,6 @@ def groupby_reduce(
         fewer than min_count non-NA values are present the result will be
         NA. Only used if skipna is set to True or defaults to True for the
         array's dtype.
-    split_out : int, optional
-        Number of chunks along group axis in output (last axis)
     method : {"map-reduce", "blockwise", "cohorts", "split-reduce"}, optional
         Strategy for reduction of dask arrays only:
           * ``"map-reduce"``:
@@ -1750,7 +1691,7 @@ def groupby_reduce(
         if kwargs["fill_value"] is None:
             kwargs["fill_value"] = agg.fill_value[agg.name]
 
-        partial_agg = partial(dask_groupby_agg, split_out=split_out, **kwargs)
+        partial_agg = partial(dask_groupby_agg, **kwargs)
 
         if method == "blockwise" and by_.ndim == 1:
             array = rechunk_for_blockwise(array, axis=-1, labels=by_)

flox/xarray.py

@@ -62,7 +62,6 @@ def xarray_reduce(
     isbin: bool | Sequence[bool] = False,
     sort: bool = True,
     dim: Dims | ellipsis = None,
-    split_out: int = 1,
     fill_value=None,
     dtype: np.typing.DTypeLike = None,
     method: str = "map-reduce",
@@ -95,8 +94,6 @@ def xarray_reduce(
     dim : hashable
         dimension name along which to reduce. If None, reduces across all
         dimensions of `by`
-    split_out : int, optional
-        Number of output chunks along grouped dimension in output.
     fill_value
         Value used for missing groups in the output i.e. when one of the labels
         in ``expected_groups`` is not actually present in ``by``.
@@ -397,7 +394,6 @@ def wrapper(array, *by, func, skipna, **kwargs):
             "func": func,
             "axis": axis,
             "sort": sort,
-            "split_out": split_out,
             "fill_value": fill_value,
             "method": method,
             "min_count": min_count,

tests/test_core.py

@@ -79,7 +79,7 @@ def test_alignment_error():
 
 
 @pytest.mark.parametrize("dtype", (float, int))
-@pytest.mark.parametrize("chunk, split_out", [(False, 1), (True, 1), (True, 2), (True, 3)])
+@pytest.mark.parametrize("chunk", [False, True])
 @pytest.mark.parametrize("expected_groups", [None, [0, 1, 2], np.array([0, 1, 2])])
 @pytest.mark.parametrize(
     "func, array, by, expected",
@@ -114,7 +114,6 @@ def test_groupby_reduce(
     expected: list[float],
     expected_groups: T_ExpectedGroupsOpt,
     chunk: bool,
-    split_out: int,
     dtype: np.typing.DTypeLike,
 ) -> None:
     array = array.astype(dtype)
@@ -137,7 +136,6 @@ def test_groupby_reduce(
         func=func,
         expected_groups=expected_groups,
         fill_value=123,
-        split_out=split_out,
         engine=engine,
     )
     g_dtype = by.dtype if expected_groups is None else np.asarray(expected_groups).dtype