BUG: Prevent nan being used in percentile (gh-18831)

Reject NaN as a percentile/quantile value. Previously NaNs could pass the range check `0 <= q <= 1`.

closes #18830

2 files changed, 24 insertions, 3 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index af5a6e45c..0bb41c270 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -3957,11 +3957,10 @@ def _quantile_is_valid(q):
     # avoid expensive reductions, relevant for arrays with < O(1000) elements
     if q.ndim == 1 and q.size < 10:
         for i in range(q.size):
-            if q[i] < 0.0 or q[i] > 1.0:
+            if not (0.0 <= q[i] <= 1.0):
                 return False
     else:
-        # faster than any()
-        if np.count_nonzero(q < 0.0) or np.count_nonzero(q > 1.0):
+        if not (np.all(0 <= q) and np.all(q <= 1)):
             return False
     return True
 
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index 761ea83a3..0b66ccf8c 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -2750,6 +2750,10 @@ class TestPercentile:
         assert_equal(p, Fraction(7, 4))
         assert_equal(type(p), Fraction)
 
+        p = np.percentile(x, [Fraction(50)])
+        assert_equal(p, np.array([Fraction(7, 4)]))
+        assert_equal(type(p), np.ndarray)
+
     def test_api(self):
         d = np.ones(5)
         np.percentile(d, 5, None, None, False)
@@ -3144,6 +3148,16 @@ class TestPercentile:
         assert_equal(np.percentile(
             a, [0.3, 0.6], (0, 2), interpolation='nearest'), b)
 
+    def test_nan_q(self):
+        # GH18830
+        with pytest.raises(ValueError, match="Percentiles must be in"):
+            np.percentile([1, 2, 3, 4.0], np.nan)
+        with pytest.raises(ValueError, match="Percentiles must be in"):
+            np.percentile([1, 2, 3, 4.0], [np.nan])
+        q = np.linspace(1.0, 99.0, 16)
+        q[0] = np.nan
+        with pytest.raises(ValueError, match="Percentiles must be in"):
+            np.percentile([1, 2, 3, 4.0], q)
 
 class TestQuantile:
     # most of this is already tested by TestPercentile
@@ -3180,6 +3194,14 @@ class TestQuantile:
         assert_equal(q, Fraction(7, 4))
         assert_equal(type(q), Fraction)
 
+        q = np.quantile(x, [Fraction(1, 2)])
+        assert_equal(q, np.array([Fraction(7, 4)]))
+        assert_equal(type(q), np.ndarray)
+
+        q = np.quantile(x, [[Fraction(1, 2)]])
+        assert_equal(q, np.array([[Fraction(7, 4)]]))
+        assert_equal(type(q), np.ndarray)
+
         # repeat with integral input but fractional quantile
         x = np.arange(8)
         assert_equal(np.quantile(x, Fraction(1, 2)), Fraction(7, 2))