ENH: stats: add array-API support to kstat/kstatvar

scipy/stats/_morestats.py

@@ -283,23 +283,25 @@ def kstat(data, n=2):
     0.00166 0.00166 -4.99e-09
     -2.88e-06 -2.88e-06 8.63e-13
     """
+    xp = array_namespace(data)
+    data = xp.asarray(data)
     if n > 4 or n < 1:
         raise ValueError("k-statistics only supported for 1<=n<=4")
     n = int(n)
-    S = np.zeros(n + 1, np.float64)
-    data = ravel(data)
-    N = data.size
+    S = xp.zeros(n + 1, dtype=xp.float64)
+    data = xp.reshape(data, (-1,))
+    N = data.shape[0]
 
     # raise ValueError on empty input
     if N == 0:
         raise ValueError("Data input must not be empty")
 
     # on nan input, return nan without warning
-    if np.isnan(np.sum(data)):
-        return np.nan
+    if xp.isnan(xp.sum(data)):
+        return _get_nan(data, xp=xp)
 
     for k in range(1, n + 1):
-        S[k] = np.sum(data**k, axis=0)
+        S[k] = xp.sum(data**k, axis=0)
     if n == 1:
         return S[1] * 1.0/N
     elif n == 2:
@@ -356,9 +358,11 @@ def kstatvar(data, n=2):
                      \frac{72 n \kappa^2_{2} \kappa_4}{(n - 1) (n - 2)} +
                      \frac{144 n \kappa_{2} \kappa^2_{3}}{(n - 1) (n - 2)} +
                      \frac{24 (n + 1) n \kappa^4_{2}}{(n - 1) (n - 2) (n - 3)}
-    """  # noqa: E501
-    data = ravel(data)
-    N = len(data)
+    """
+    xp = array_namespace(data)
+    xp.asarray(data)
+    data = xp.reshape(data, (-1,))
+    N = data.shape[0]
     if n == 1:
         return kstat(data, n=2) * 1.0/N
     elif n == 2:

scipy/stats/tests/test_morestats.py

@@ -21,10 +21,14 @@
 from .._hypotests import _get_wilcoxon_distr, _get_wilcoxon_distr2
 from scipy.stats._binomtest import _binary_search_for_binom_tst
 from scipy.stats._distr_params import distcont
+
 from scipy.conftest import array_api_compatible
 from scipy._lib._array_api import (array_namespace, xp_assert_close, xp_assert_less,
                                    SCIPY_ARRAY_API, xp_assert_equal)
 
+
+skip_xp_backends = pytest.mark.skip_xp_backends
+
 distcont = dict(distcont)  # type: ignore
 
 # Matplotlib is not a scipy dependency but is optionally used in probplot, so
@@ -1661,48 +1665,55 @@ def test_permutation_method(self, size):
         assert_equal(res.pvalue, ref.pvalue)  # random_state used
 
 
+@array_api_compatible
 class TestKstat:
-    def test_moments_normal_distribution(self):
+    def test_moments_normal_distribution(self, xp):
         np.random.seed(32149)
-        data = np.random.randn(12345)
-        moments = [stats.kstat(data, n) for n in [1, 2, 3, 4]]
+        data = xp.asarray(np.random.randn(12345))
+        moments = xp.asarray([stats.kstat(data, n) for n in [1, 2, 3, 4]])
 
-        expected = [0.011315, 1.017931, 0.05811052, 0.0754134]
-        assert_allclose(moments, expected, rtol=1e-4)
+        expected = xp.asarray([0.011315, 1.017931, 0.05811052, 0.0754134],
+                              dtype=data.dtype)
+        xp_assert_close(moments, expected, rtol=1e-4)
 
         # test equivalence with `stats.moment`
         m1 = stats.moment(data, order=1)
         m2 = stats.moment(data, order=2)
         m3 = stats.moment(data, order=3)
-        assert_allclose((m1, m2, m3), expected[:-1], atol=0.02, rtol=1e-2)
+        xp_assert_close(xp.asarray((m1, m2, m3)), expected[:-1], atol=0.02, rtol=1e-2)
 
-    def test_empty_input(self):
-        assert_raises(ValueError, stats.kstat, [])
+    def test_empty_input(self, xp):
+        assert_raises(ValueError, stats.kstat, xp.asarray([]))
 
-    def test_nan_input(self):
-        data = np.arange(10.)
-        data[6] = np.nan
+    def test_nan_input(self, xp):
+        data = xp.arange(10.)
+        data[6] = xp.nan
 
-        assert_equal(stats.kstat(data), np.nan)
+        xp_assert_equal(stats.kstat(data), xp.asarray(xp.nan))
 
-    def test_kstat_bad_arg(self):
+    @skip_xp_backends(np_only=True,
+                      reasons=['input validation of `n` does not depend on backend'])
+    def test_kstat_bad_arg(self, xp):
         # Raise ValueError if n > 4 or n < 1.
         data = np.arange(10)
         for n in [0, 4.001]:
             assert_raises(ValueError, stats.kstat, data, n=n)
 
 
+@array_api_compatible
 class TestKstatVar:
-    def test_empty_input(self):
-        assert_raises(ValueError, stats.kstatvar, [])
+    def test_empty_input(self, xp):
+        assert_raises(ValueError, stats.kstatvar, xp.asarray([]))
 
-    def test_nan_input(self):
-        data = np.arange(10.)
-        data[6] = np.nan
+    def test_nan_input(self, xp):
+        data = xp.arange(10.)
+        data[6] = xp.nan
 
-        assert_equal(stats.kstat(data), np.nan)
+        xp_assert_equal(stats.kstat(data), xp.asarray(xp.nan))
 
-    def test_bad_arg(self):
+    @skip_xp_backends(np_only=True,
+                      reasons=['input validation of `n` does not depend on backend'])
+    def test_bad_arg(self, xp):
         # Raise ValueError is n is not 1 or 2.
         data = [1]
         n = 10