Merge pull request #5633 from jreback/setitem_empty

BUG: make sure partial setting with a Series like works with a completly empty frame (GH5632)

Author: jreback

doc/source/release.rst

@@ -246,7 +246,7 @@ API Changes
     (:issue:`4390`)
   - allow ``ix/loc`` for Series/DataFrame/Panel to set on any axis even when
     the single-key is not currently contained in the index for that axis
-    (:issue:`2578`, :issue:`5226`)
+    (:issue:`2578`, :issue:`5226`, :issue:`5632`)
   - Default export for ``to_clipboard`` is now csv with a sep of `\t` for
     compat (:issue:`3368`)
   - ``at`` now will enlarge the object inplace (and return the same)

pandas/core/frame.py

@@ -1895,9 +1895,16 @@ def _ensure_valid_index(self, value):
         passed value
         """
         if not len(self.index):
+
+            # GH5632, make sure that we are a Series convertible
+            try:
+                value = Series(value)
+            except:
+                pass
+
             if not isinstance(value, Series):
                 raise ValueError('Cannot set a frame with no defined index '
-                                 'and a non-series')
+                                 'and a value that cannot be converted to a Series')
             self._data.set_axis(1, value.index.copy(), check_axis=False)
 
     def _set_item(self, key, value):

pandas/tests/test_indexing.py

@@ -1635,6 +1635,42 @@ def f():
             df.loc[:,1] = 1
         self.assertRaises(ValueError, f)
 
+        # these work as they don't really change
+        # anything but the index
+        # GH5632
+        expected = DataFrame(columns=['foo'])
+        def f():
+            df = DataFrame()
+            df['foo'] = Series([])
+            return df
+        assert_frame_equal(f(), expected)
+        def f():
+            df = DataFrame()
+            df['foo'] = Series(df.index)
+            return df
+        assert_frame_equal(f(), expected)
+        def f():
+            df = DataFrame()
+            df['foo'] = Series(range(len(df)))
+            return df
+        assert_frame_equal(f(), expected)
+        def f():
+            df = DataFrame()
+            df['foo'] = []
+            return df
+        assert_frame_equal(f(), expected)
+        def f():
+            df = DataFrame()
+            df['foo'] = df.index
+            return df
+        assert_frame_equal(f(), expected)
+        def f():
+            df = DataFrame()
+            df['foo'] = range(len(df))
+            return df
+        assert_frame_equal(f(), expected)
+
+        df = DataFrame()
         df2 = DataFrame()
         df2[1] = Series([1],index=['foo'])
         df.loc[:,1] = Series([1],index=['foo'])