Add tests for sparse mean_var accuracy

pyproject.toml

@@ -85,6 +85,7 @@ overrides.matrix.extras.features = [
 ]
 overrides.matrix.extras.dependencies = [
   { if = [ "full" ], value = "scipy-stubs" },
+  { if = [ "full" ], value = "scikit-learn" },
 ]
 
 [[tool.hatch.envs.hatch-test.matrix]]

tests/test_stats.py

@@ -223,6 +223,42 @@ def test_mean_var(
     np.testing.assert_array_almost_equal(var, var_expected)  # type: ignore[arg-type]
 
 
+@pytest.mark.skipif(not find_spec("sklearn"), reason="sklearn not installed")
+@pytest.mark.array_type(Flags.Sparse, skip=Flags.Matrix | Flags.Dask | Flags.Disk | Flags.Gpu)
+@pytest.mark.parametrize("axis", [0, 1])
+def test_mean_var_sparse_64(array_type: ArrayType[types.CSArray], axis: Literal[0, 1]) -> None:
+    """Test that we’re equivalent for 64 bit."""
+    from sklearn.utils.sparsefuncs import mean_variance_axis
+
+    mtx = array_type.random((10000, 1000), dtype=np.float64)
+
+    mean_fau, var_fau = stats.mean_var(mtx, axis=axis)
+    mean_skl, var_skl = mean_variance_axis(mtx, axis)
+
+    np.testing.assert_allclose(mean_fau, mean_skl, rtol=1.0e-5, atol=1.0e-8)
+    np.testing.assert_allclose(var_fau, var_skl, rtol=1.0e-5, atol=1.0e-8)
+
+
+@pytest.mark.skipif(not find_spec("sklearn"), reason="sklearn not installed")
+@pytest.mark.array_type(Flags.Sparse, skip=Flags.Matrix | Flags.Dask | Flags.Disk | Flags.Gpu)
+def test_mean_var_sparse_32(array_type: ArrayType[types.CSArray]) -> None:
+    """Test whether we are more accurate for 32 bit."""
+    from sklearn.utils.sparsefuncs import mean_variance_axis
+
+    mtx64 = array_type.random((10000, 1000), dtype=np.float64)
+    mtx32 = mtx64.astype(np.float32)
+
+    fau, skl = {}, {}
+    for n_bit, mtx in [(32, mtx32), (64, mtx64)]:
+        fau[n_bit] = stats.mean_var(mtx, axis=0)
+        skl[n_bit] = mean_variance_axis(mtx, 0)
+
+    for stat, _ in enumerate(["mean", "var"]):
+        resid_fau = np.mean(np.abs(fau[64][stat] - fau[32][stat]))
+        resid_skl = np.mean(np.abs(skl[64][stat] - skl[32][stat]))
+        assert resid_fau < resid_skl
+
+
 @pytest.mark.array_type(skip={Flags.Disk, *ATS_CUPY_SPARSE})
 @pytest.mark.parametrize(
     ("axis", "expected"),

typings/sklearn/utils/sparsefuncs.pyi

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: MPL-2.0
+from typing import Literal
+
+import numpy as np
+from numpy.typing import NDArray
+from scipy.sparse import csc_array, csc_matrix, csr_array, csr_matrix
+
+def mean_variance_axis(
+    X: csc_array | csc_matrix | csr_array | csr_matrix,  # noqa: N803
+    axis: Literal[0, 1],
+    weights: NDArray[np.floating] | None = None,
+    return_sum_weights: bool = False,
+) -> tuple[NDArray[np.float64], NDArray[np.float64]]: ...