BUG: applymap on empty DataFrame returns Series (#8222)

doc/source/whatsnew/v0.20.0.txt

@@ -237,6 +237,7 @@ Other API Changes
 
 - ``CParserError`` has been renamed to ``ParserError`` in ``pd.read_csv`` and will be removed in the future (:issue:`12665`)
 - ``SparseArray.cumsum()`` and ``SparseSeries.cumsum()`` will now always return ``SparseArray`` and ``SparseSeries`` respectively (:issue:`12855`)
+- ``DataFrame.applymap()`` with an empty ``DataFrame`` will return a copy of the empty ``DataFrame`` instead of a ``Series`` (:issue:`8222`)
 
 .. _whatsnew_0200.deprecations:
 
@@ -286,7 +287,6 @@ Bug Fixes
 - Bug in ``DataFrame.sort_values()`` when sorting by multiple columns where one column is of type ``int64`` and contains ``NaT`` (:issue:`14922`)
 
 
-
 - Bug in ``pd.read_msgpack()`` in which ``Series`` categoricals were being improperly processed (:issue:`14901`)
 - Bug in ``Series.ffill()`` with mixed dtypes containing tz-aware datetimes. (:issue:`14956`)
 

pandas/core/frame.py

@@ -4288,6 +4288,8 @@ def applymap(self, func):
 
         # if we have a dtype == 'M8[ns]', provide boxed values
         def infer(x):
+            if x.empty:
+                return lib.map_infer(x, func)
             return lib.map_infer(x.asobject, func)
 
         return self.apply(infer)

pandas/tests/frame/test_apply.py

@@ -405,6 +405,16 @@ def test_applymap(self):
         for f in ['datetime', 'timedelta']:
             self.assertEqual(result.loc[0, f], str(df.loc[0, f]))
 
+        # GH 8222
+        empty_frames = [pd.DataFrame(),
+                        pd.DataFrame(columns=list('ABC')),
+                        pd.DataFrame(index=list('ABC')),
+                        pd.DataFrame({'A': [], 'B': [], 'C': []})]
+        for frame in empty_frames:
+            for func in [round, lambda x: x]:
+                result = frame.applymap(func)
+                tm.assert_frame_equal(result, frame)
+
     def test_applymap_box(self):
         # ufunc will not be boxed. Same test cases as the test_map_box
         df = pd.DataFrame({'a': [pd.Timestamp('2011-01-01'),