BUG: recfunctions.join_by fails for colliding values with different dtypes

Fixes #9338

1 files changed, 13 insertions, 0 deletions

diff --git a/numpy/lib/tests/test_recfunctions.py b/numpy/lib/tests/test_recfunctions.py
index e9cfa4993..a5d15cb24 100644
--- a/numpy/lib/tests/test_recfunctions.py
+++ b/numpy/lib/tests/test_recfunctions.py
@@ -656,6 +656,19 @@ class TestJoinBy(TestCase):
         b = np.ones(3, dtype=[('c', 'u1'), ('b', 'f4'), ('a', 'i4')])
         assert_raises(ValueError, join_by, ['a', 'b', 'b'], a, b)
 
+    def test_same_name_different_dtypes(self):
+        # gh-9338
+        a_dtype = np.dtype([('key', 'S10'), ('value', '<f4')])
+        b_dtype = np.dtype([('key', 'S10'), ('value', '<f8')])
+        expected_dtype = np.dtype([
+            ('key', '|S10'), ('value1', '<f4'), ('value2', '<f8')])
+
+        a = np.array([('Sarah',  8.0), ('John', 6.0)], dtype=a_dtype)
+        b = np.array([('Sarah', 10.0), ('John', 7.0)], dtype=b_dtype)
+        res = join_by('key', a, b)
+
+        assert_equal(res.dtype, expected_dtype)
+
 
 class TestJoinBy2(TestCase):
     @classmethod