Fix maybe_convert_numeric for unhashable objects

Author: Roger Thomas

doc/source/whatsnew/v0.18.2.txt

@@ -317,6 +317,7 @@ Bug Fixes
 - Bug in ``groupby`` where ``apply`` returns different result depending on whether first result is ``None`` or not (:issue:`12824`)
 
 
+- Bug in ``pd.to_numeric`` when ``errors='coerce'`` and input contains non-hashable objects (:issue:`13324`)
 
 
 - Bug in ``Categorical.remove_unused_categories()`` changes ``.codes`` dtype to platform int (:issue:`13261`)

pandas/src/inference.pyx

@@ -569,7 +569,7 @@ def maybe_convert_numeric(object[:] values, set na_values,
     for i in range(n):
         val = values[i]
 
-        if val in na_values:
+        if val.__hash__ is not None and val in na_values:
             floats[i] = complexes[i] = nan
             seen_float = True
         elif util.is_float_object(val):

pandas/tests/test_infer_and_convert.py

@@ -102,6 +102,12 @@ def test_scientific_no_exponent(self):
         result = lib.maybe_convert_numeric(arr, set(), False, True)
         self.assertTrue(np.all(np.isnan(result)))
 
+    def test_convert_non_hashable(self):
+        # Test for Bug #13324
+        arr = np.array([[10.0, 2], 1.0, 'apple'])
+        result = lib.maybe_convert_numeric(arr, set(), False, True)
+        tm.assert_numpy_array_equal(result, np.array([np.nan, 1.0, np.nan]))
+
 
 class TestTypeInference(tm.TestCase):
     _multiprocess_can_split_ = True

pandas/tools/tests/test_util.py

@@ -279,6 +279,18 @@ def test_period(self):
         # res = pd.to_numeric(pd.Series(idx, name='xxx'))
         # tm.assert_series_equal(res, pd.Series(idx.asi8, name='xxx'))
 
+    def test_non_hashable(self):
+        # Test for Bug #13324
+        s = pd.Series([[10.0, 2], 1.0, 'apple'])
+        res = pd.to_numeric(s, errors='coerce')
+        tm.assert_series_equal(res, pd.Series([np.nan, 1.0, np.nan]))
+
+        res = pd.to_numeric(s, errors='ignore')
+        tm.assert_series_equal(res, pd.Series([[10.0, 2], 1.0, 'apple']))
+
+        with self.assertRaisesRegexp(TypeError, "Invalid object type"):
+            pd.to_numeric(s)
+
 
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],