Add test for multiple

Author: Roger Thomas

pandas/src/inference.pyx

@@ -1,3 +1,4 @@
+from decimal import Decimal
 import sys
 cimport util
 from tslib import NaT, get_timezone
@@ -673,6 +674,9 @@ def maybe_convert_numeric(object[:] values, set na_values,
         elif util.is_complex_object(val):
             complexes[i] = val
             seen_complex = True
+        elif isinstance(val, Decimal):
+            floats[i] = complexes[i] = val
+            seen_float = True
         else:
             try:
                 status = floatify(val, &fval, &maybe_int)

pandas/tools/tests/test_util.py

@@ -211,13 +211,23 @@ def test_numeric(self):
 
         # GH 14827
         df = pd.DataFrame(dict(
-            a=[1.2, decimal.Decimal(3.14), decimal.Decimal("infinity"), '0.1']
+            a=[1.2, decimal.Decimal(3.14), decimal.Decimal("infinity"), '0.1'],
+            b=[1.0, 2.0, 3.0, 4.0],
         ))
-        df['a'] = df['a'].apply(to_numeric)
         expected = pd.DataFrame(dict(
-            a=[1.2, 3.14, np.inf, 0.1]
+            a=[1.2, 3.14, np.inf, 0.1],
+            b=[1.0, 2.0, 3.0, 4.0],
         ))
-        tm.assert_frame_equal(df, expected)
+
+        # Test to_numeric over one column
+        df_copy = df.copy()
+        df_copy['a'] = df_copy['a'].apply(to_numeric)
+        tm.assert_frame_equal(df_copy, expected)
+
+        # Test to_numeric over multiple columns
+        df_copy = df.copy()
+        df_copy[['a', 'b']] = df_copy[['a', 'b']].apply(to_numeric)
+        tm.assert_frame_equal(df_copy, expected)
 
     def test_all_nan(self):
         s = pd.Series(['a', 'b', 'c'])