ENH: Add support for Fraction to percentile and quantile

With true division available, using `.0` to convert integers to floats offers no value, and harms compatibility with precise rational types.

2 files changed, 39 insertions, 2 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 2e82fa075..cab680751 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -3706,7 +3706,8 @@ def percentile(a, q, axis=None, out=None,
         plt.show()
 
     """
-    q = np.true_divide(q, 100.0)  # handles the asarray for us too
+    q = np.true_divide(q, 100)
+    q = asanyarray(q)  # undo any decay that the ufunc performed (see gh-13105)
     if not _quantile_is_valid(q):
         raise ValueError("Percentiles must be in the range [0, 100]")
     return _quantile_unchecked(
@@ -3924,7 +3925,7 @@ def _quantile_ureduce_func(a, q, axis=None, out=None, overwrite_input=False,
             indices_above = concatenate((indices_above, [-1]))
 
         weights_above = indices - indices_below
-        weights_below = 1.0 - weights_above
+        weights_below = 1 - weights_above
 
         weights_shape = [1, ] * ap.ndim
         weights_shape[axis] = len(indices)
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index e2c24a123..6d32c365a 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -5,6 +5,7 @@ import warnings
 import sys
 import decimal
 import types
+from fractions import Fraction
 import pytest
 
 import numpy as np
@@ -2508,6 +2509,21 @@ class TestPercentile(object):
         assert_equal(np.percentile(x, 0), np.nan)
         assert_equal(np.percentile(x, 0, interpolation='nearest'), np.nan)
 
+    def test_fraction(self):
+        x = [Fraction(i, 2) for i in np.arange(8)]
+
+        p = np.percentile(x, Fraction(0))
+        assert_equal(p, Fraction(0))
+        assert_equal(type(p), Fraction)
+
+        p = np.percentile(x, Fraction(100))
+        assert_equal(p, Fraction(7, 2))
+        assert_equal(type(p), Fraction)
+
+        p = np.percentile(x, Fraction(50))
+        assert_equal(p, Fraction(7, 4))
+        assert_equal(type(p), Fraction)
+
     def test_api(self):
         d = np.ones(5)
         np.percentile(d, 5, None, None, False)
@@ -2912,6 +2928,26 @@ class TestQuantile(object):
         assert_equal(np.quantile(x, 1), 3.5)
         assert_equal(np.quantile(x, 0.5), 1.75)
 
+    def test_fraction(self):
+        # fractional input, integral quantile
+        x = [Fraction(i, 2) for i in np.arange(8)]
+
+        q = np.quantile(x, 0)
+        assert_equal(q, 0)
+        assert_equal(type(q), Fraction)
+
+        q = np.quantile(x, 1)
+        assert_equal(q, Fraction(7, 2))
+        assert_equal(type(q), Fraction)
+
+        q = np.quantile(x, Fraction(1, 2))
+        assert_equal(q, Fraction(7, 4))
+        assert_equal(type(q), Fraction)
+
+        # repeat with integral input but fractional quantile
+        x = np.arange(8)
+        assert_equal(np.quantile(x, Fraction(1, 2)), Fraction(7, 2))
+
     def test_no_p_overwrite(self):
         # this is worth retesting, because quantile does not make a copy
         p0 = np.array([0, 0.75, 0.25, 0.5, 1.0])