Fix Dask handling for chunks with 1-wide dimension

src/fast_array_utils/_validation.py

@@ -9,7 +9,7 @@ def validate_axis(ndim: int, axis: int | None) -> None:
     if axis is None:
         return
     if not isinstance(axis, int | np.integer):  # pragma: no cover
-        msg = "axis must be integer or None."
+        msg = f"axis must be integer or None, not {axis=!r}."
         raise TypeError(msg)
     if axis == 0 and ndim == 1:
         raise AxisError(axis, ndim, "use axis=None for 1D arrays")

src/fast_array_utils/stats/__init__.py

@@ -227,19 +227,56 @@ def mean_var(
 # https://github.com/scverse/fast-array-utils/issues/52
 @overload
 def sum(
-    x: CpuArray | GpuArray | DiskArray, /, *, axis: None = None, dtype: DTypeLike | None = None
+    x: CpuArray | DiskArray,
+    /,
+    *,
+    axis: None = None,
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> np.number[Any]: ...
 @overload
 def sum(
-    x: CpuArray | DiskArray, /, *, axis: Literal[0, 1], dtype: DTypeLike | None = None
+    x: CpuArray | DiskArray,
+    /,
+    *,
+    axis: Literal[0, 1],
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> NDArray[Any]: ...
+
+
 @overload
 def sum(
-    x: GpuArray, /, *, axis: Literal[0, 1], dtype: DTypeLike | None = None
+    x: GpuArray,
+    /,
+    *,
+    axis: None = None,
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: Literal[False] = False,
+) -> np.number[Any]: ...
+@overload
+def sum(
+    x: GpuArray, /, *, axis: None, dtype: DTypeLike | None = None, keep_cupy_as_array: Literal[True]
+) -> types.CupyArray: ...
+@overload
+def sum(
+    x: GpuArray,
+    /,
+    *,
+    axis: Literal[0, 1],
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> types.CupyArray: ...
+
+
 @overload
 def sum(
-    x: types.DaskArray, /, *, axis: Literal[0, 1, None] = None, dtype: DTypeLike | None = None
+    x: types.DaskArray,
+    /,
+    *,
+    axis: Literal[0, 1, None] = None,
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> types.DaskArray: ...
 
 
@@ -249,6 +286,7 @@ def sum(
     *,
     axis: Literal[0, 1, None] = None,
     dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> NDArray[Any] | types.CupyArray | np.number[Any] | types.DaskArray:
     """Sum over both or one axis.
 
@@ -286,4 +324,4 @@ def sum(
     from ._sum import sum_
 
     validate_axis(x.ndim, axis)
-    return sum_(x, axis=axis, dtype=dtype)
+    return sum_(x, axis=axis, dtype=dtype, keep_cupy_as_array=keep_cupy_as_array)

src/fast_array_utils/stats/_sum.py

@@ -2,20 +2,25 @@
 from __future__ import annotations
 
 from functools import partial, singledispatch
-from typing import TYPE_CHECKING, cast
+from typing import TYPE_CHECKING, Literal, cast
 
 import numpy as np
+from numpy.exceptions import AxisError
 
 from .. import types
 
 
 if TYPE_CHECKING:
-    from typing import Any, Literal
+    from typing import Any, Literal, TypeAlias
 
     from numpy.typing import DTypeLike, NDArray
 
     from ..typing import CpuArray, DiskArray, GpuArray
 
+    ComplexAxis: TypeAlias = (
+        tuple[Literal[0], Literal[1]] | tuple[Literal[0, 1]] | Literal[0, 1, None]
+    )
+
 
 @singledispatch
 def sum_(
@@ -24,7 +29,9 @@ def sum_(
     *,
     axis: Literal[0, 1, None] = None,
     dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> NDArray[Any] | np.number[Any] | types.CupyArray | types.DaskArray:
+    del keep_cupy_as_array
     if TYPE_CHECKING:
         # these are never passed to this fallback function, but `singledispatch` wants them
         assert not isinstance(
@@ -37,16 +44,31 @@ def sum_(
 
 @sum_.register(types.CupyArray | types.CupyCSMatrix)  # type: ignore[call-overload,misc]
 def _sum_cupy(
-    x: GpuArray, /, *, axis: Literal[0, 1, None] = None, dtype: DTypeLike | None = None
+    x: GpuArray,
+    /,
+    *,
+    axis: Literal[0, 1, None] = None,
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> types.CupyArray | np.number[Any]:
     arr = cast("types.CupyArray", np.sum(x, axis=axis, dtype=dtype))
-    return cast("np.number[Any]", arr.get()[()]) if axis is None else arr.squeeze()
+    return (
+        cast("np.number[Any]", arr.get()[()])
+        if not keep_cupy_as_array and axis is None
+        else arr.squeeze()
+    )
 
 
 @sum_.register(types.CSBase)  # type: ignore[call-overload,misc]
 def _sum_cs(
-    x: types.CSBase, /, *, axis: Literal[0, 1, None] = None, dtype: DTypeLike | None = None
+    x: types.CSBase,
+    /,
+    *,
+    axis: Literal[0, 1, None] = None,
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> NDArray[Any] | np.number[Any]:
+    del keep_cupy_as_array
     import scipy.sparse as sp
 
     if isinstance(x, types.CSMatrix):
@@ -59,49 +81,92 @@ def _sum_cs(
 
 @sum_.register(types.DaskArray)
 def _sum_dask(
-    x: types.DaskArray, /, *, axis: Literal[0, 1, None] = None, dtype: DTypeLike | None = None
+    x: types.DaskArray,
+    /,
+    *,
+    axis: Literal[0, 1, None] = None,
+    dtype: DTypeLike | None = None,
+    keep_cupy_as_array: bool = False,
 ) -> types.DaskArray:
     import dask.array as da
 
-    from . import sum
-
     if isinstance(x._meta, np.matrix):  # pragma: no cover  # noqa: SLF001
         msg = "sum does not support numpy matrices"
         raise TypeError(msg)
 
-    def sum_drop_keepdims(
-        a: CpuArray,
-        /,
-        *,
-        axis: tuple[Literal[0], Literal[1]] | Literal[0, 1, None] = None,
-        dtype: DTypeLike | None = None,
-        keepdims: bool = False,
-    ) -> NDArray[Any] | types.CupyArray:
-        del keepdims
-        if a.ndim == 1:
-            axis = None
-        else:
-            match axis:
-                case (0, 1) | (1, 0):
-                    axis = None
-                case (0 | 1 as n,):
-                    axis = n
-                case tuple():  # pragma: no cover
-                    msg = f"`sum` can only sum over `axis=0|1|(0,1)` but got {axis} instead"
-                    raise ValueError(msg)
-        rv = sum(a, axis=axis, dtype=dtype)
-        shape = (1,) if a.ndim == 1 else (1, 1 if rv.shape == () else len(rv))  # type: ignore[arg-type]
-        return np.reshape(rv, shape)
-
     if dtype is None:
         # Explicitly use numpy result dtype (e.g. `NDArray[bool].sum().dtype == int64`)
         dtype = np.zeros(1, dtype=x.dtype).sum().dtype
 
-    return da.reduction(
+    rv = da.reduction(
         x,
-        sum_drop_keepdims,  # type: ignore[arg-type]
-        partial(np.sum, dtype=dtype),  # pyright: ignore[reportArgumentType]
+        sum_dask_inner,  # type: ignore[arg-type]
+        partial(sum_dask_inner, dtype=dtype),  # pyright: ignore[reportArgumentType]
         axis=axis,
         dtype=dtype,
         meta=np.array([], dtype=dtype),
     )
+
+    if axis is not None or (
+        isinstance(rv._meta, types.CupyArray)  # noqa: SLF001
+        and keep_cupy_as_array
+    ):
+        return rv
+
+    def to_scalar(a: types.CupyArray | NDArray[Any]) -> np.number[Any]:
+        if isinstance(a, types.CupyArray):
+            a = a.get()
+        return a.reshape(())[()]  # type: ignore[return-value]
+
+    return rv.map_blocks(to_scalar, meta=x.dtype.type(0))  # type: ignore[arg-type]
+
+
+def sum_dask_inner(
+    a: CpuArray | GpuArray,
+    /,
+    *,
+    axis: ComplexAxis = None,
+    dtype: DTypeLike | None = None,
+    keepdims: bool = False,
+) -> NDArray[Any] | types.CupyArray:
+    from . import sum
+
+    axis = normalize_axis(axis, a.ndim)
+    rv = sum(a, axis=axis, dtype=dtype, keep_cupy_as_array=True)  # type: ignore[misc,arg-type]
+    shape = get_shape(rv, axis=axis, keepdims=keepdims)
+    return cast("NDArray[Any] | types.CupyArray", rv.reshape(shape))
+
+
+def normalize_axis(axis: ComplexAxis, ndim: int) -> Literal[0, 1, None]:
+    """Adapt `axis` parameter passed by Dask to what we support."""
+    match axis:
+        case int() | None:
+            pass
+        case (0 | 1,):
+            axis = axis[0]
+        case (0, 1) | (1, 0):
+            axis = None
+        case _:  # pragma: no cover
+            raise AxisError(axis, ndim)  # type: ignore[call-overload]
+    if axis == 0 and ndim == 1:
+        return None  # dask’s aggregate doesn’t know we don’t accept `axis=0` for 1D arrays
+    return axis
+
+
+def get_shape(
+    a: NDArray[Any] | np.number[Any] | types.CupyArray, *, axis: Literal[0, 1, None], keepdims: bool
+) -> tuple[int] | tuple[int, int]:
+    """Get the output shape of an axis-flattening operation."""
+    match keepdims, a.ndim:
+        case False, 0:
+            return (1,)
+        case True, 0:
+            return (1, 1)
+        case False, 1:
+            return (a.size,)
+        case True, 1:
+            assert axis is not None
+            return (1, a.size) if axis == 0 else (a.size, 1)
+    # pragma: no cover
+    msg = f"{keepdims=}, {type(a)}"
+    raise AssertionError(msg)

tests/test_stats.py

@@ -97,7 +97,7 @@ def dtype_arg(request: pytest.FixtureRequest) -> type[DTypeOut] | None:
 
 @pytest.fixture
 def np_arr(dtype_in: type[DTypeIn], ndim: Literal[1, 2]) -> NDArray[DTypeIn]:
-    np_arr = cast("NDArray[DTypeIn]", np.array([[1, 2, 3], [4, 5, 6]], dtype=dtype_in))
+    np_arr = cast("NDArray[DTypeIn]", np.array([[1, 0], [3, 0], [5, 6]], dtype=dtype_in))
     np_arr.flags.writeable = False
     if ndim == 1:
         np_arr = np_arr.flatten()
@@ -165,6 +165,28 @@ def test_sum(
     np.testing.assert_array_equal(sum_, expected)
 
 
+@pytest.mark.parametrize(
+    "data",
+    [
+        pytest.param([[1, 0], [3, 0], [5, 6]], id="3x2"),
+        pytest.param([[1, 2, 3], [4, 5, 6]], id="2x3"),
+        pytest.param([[1, 0], [0, 2]], id="2x2"),
+    ],
+)
+@pytest.mark.parametrize("axis", [0, 1])
+@pytest.mark.array_type(Flags.Dask)
+def test_sum_dask_shapes(
+    array_type: ArrayType[types.DaskArray], axis: Literal[0, 1], data: list[list[int]]
+) -> None:
+    np_arr = np.array(data, dtype=np.float32)
+    arr = array_type(np_arr)
+    assert 1 in arr.chunksize, "This test is supposed to test 1×n and n×1 chunk sizes"
+    sum_ = cast("NDArray[Any] | types.CupyArray", stats.sum(arr, axis=axis).compute())
+    if isinstance(sum_, types.CupyArray):
+        sum_ = sum_.get()
+    np.testing.assert_almost_equal(np_arr.sum(axis=axis), sum_)
+
+
 @pytest.mark.array_type(skip=ATS_SPARSE_DS)
 def test_mean(
     array_type: ArrayType[Array], axis: Literal[0, 1, None], np_arr: NDArray[DTypeIn]

typings/cupy/_core/core.pyi

@@ -8,13 +8,15 @@ from numpy.typing import NDArray
 class ndarray:
     dtype: np.dtype[Any]
     shape: tuple[int, ...]
+    size: int
     ndim: int
 
     # cupy-specific
     def get(self) -> NDArray[Any]: ...
 
     # operators
     def __array__(self) -> NDArray[Any]: ...
+    def __len__(self) -> int: ...
     def __getitem__(  # never returns scalars
         self, index: int | slice | EllipsisType | tuple[int | slice | EllipsisType | None, ...]
     ) -> Self: ...
@@ -28,6 +30,7 @@ class ndarray:
     def all(self, axis: None = None) -> np.bool: ...
     @overload
     def all(self, axis: int) -> ndarray: ...
+    def reshape(self, shape: tuple[int, ...] | int) -> ndarray: ...
     def squeeze(self, axis: int | None = None) -> Self: ...
     def ravel(self, order: Literal["C", "F", "A", "K"] = "C") -> Self: ...
     def flatten(self, order: Literal["C", "F", "A", "K"] = "C") -> Self: ...

typings/dask/array/core.pyi

@@ -44,6 +44,8 @@ class Array:
     # dask methods and attrs
     _meta: _Array
     blocks: BlockView
+    chunks: tuple[tuple[int, ...], ...]
+    chunksize: tuple[int, ...]
 
     def compute(self) -> _Array: ...
     def visualize(