BUG: from_dict ignored order of OrderedDict (#8425)

Author: mazayo

doc/source/whatsnew/v0.25.0.rst

@@ -633,6 +633,7 @@ Indexing
 - Bug in which :meth:`DataFrame.to_csv` caused a segfault for a reindexed data frame, when the indices were single-level :class:`MultiIndex` (:issue:`26303`).
 - Fixed bug where assigning a :class:`arrays.PandasArray` to a :class:`pandas.core.frame.DataFrame` would raise error (:issue:`26390`)
 - Allow keyword arguments for callable local reference used in the :meth:`DataFrame.query` string (:issue:`26426`)
+- Bug in which :meth:`DataFrame.from_dict` ignored order of OrderedDict when orient='index' (:issue:`8425`).
 
 
 Missing

pandas/core/internals/construction.py

@@ -301,8 +301,10 @@ def extract_index(data):
             raise ValueError('If using all scalar values, you must pass'
                              ' an index')
 
-        if have_series or have_dicts:
+        if have_series:
             index = _union_indexes(indexes)
+        elif have_dicts:
+            index = _union_indexes(indexes, sort=False)
 
         if have_raw_arrays:
             lengths = list(set(raw_lengths))

pandas/tests/frame/test_constructors.py

@@ -483,7 +483,7 @@ def test_constructor_subclass_dict(self):
             dct.update(v.to_dict())
             data[k] = dct
         frame = DataFrame(data)
-        tm.assert_frame_equal(self.frame.sort_index(), frame)
+        tm.assert_frame_equal(self.frame, frame)
 
     def test_constructor_dict_block(self):
         expected = np.array([[4., 3., 2., 1.]])
@@ -1153,7 +1153,7 @@ def test_constructor_list_of_series(self):
 
         sdict = OrderedDict(zip(['x', 'Unnamed 0'], data))
         expected = DataFrame.from_dict(sdict, orient='index')
-        tm.assert_frame_equal(result.sort_index(), expected)
+        tm.assert_frame_equal(result, expected)
 
         # none named
         data = [OrderedDict([['a', 1.5], ['b', 3], ['c', 4], ['d', 6]]),
@@ -1288,7 +1288,7 @@ def test_constructor_list_of_namedtuples(self):
     def test_constructor_orient(self):
         data_dict = self.mixed_frame.T._series
         recons = DataFrame.from_dict(data_dict, orient='index')
-        expected = self.mixed_frame.sort_index()
+        expected = self.mixed_frame.reindex(recons.index)
         tm.assert_frame_equal(recons, expected)
 
         # dict of sequence
@@ -1298,6 +1298,16 @@ def test_constructor_orient(self):
         xp = DataFrame.from_dict(a).T.reindex(list(a.keys()))
         tm.assert_frame_equal(rs, xp)
 
+    def test_constructor_from_ordered_dict(self):
+        # GH8425
+        a = OrderedDict([
+            ('one', OrderedDict([('col_a', 'foo1'), ('col_b', 'bar1')])),
+            ('two', OrderedDict([('col_a', 'foo2'), ('col_b', 'bar2')])),
+            ('three', OrderedDict([('col_a', 'foo3'), ('col_b', 'bar3')]))])
+        expected = DataFrame.from_dict(a, orient='columns').T
+        result = DataFrame.from_dict(a, orient='index')
+        tm.assert_frame_equal(result, expected)
+
     def test_from_dict_columns_parameter(self):
         # GH 18529
         # Test new columns parameter for from_dict that was added to make

pandas/tests/test_lib.py

@@ -203,3 +203,15 @@ def test_get_reverse_indexer(self):
 def test_cache_readonly_preserve_docstrings():
     # GH18197
     assert Index.hasnans.__doc__ is not None
+
+
+def test_fast_unique_multiple_list_with_sort():
+    keys = [['p', 'a'], ['n', 'd'], ['a', 's']]
+
+    expected = np.array(['a', 'd', 'n', 'p', 's'])
+    result = lib.fast_unique_multiple_list(keys, sort=True)
+    tm.assert_numpy_array_equal(np.array(result), expected)
+
+    expected = np.array(['p', 'a', 'n', 'd', 's'])
+    result = lib.fast_unique_multiple_list(keys, sort=False)
+    tm.assert_numpy_array_equal(np.array(result), expected)