Merge pull request #3564 from jreback/GH3562

BUG: Duplicate indexes with and empty DataFrame.from_records will return a correct frame (GH3562)

Author: jreback

RELEASE.rst

@@ -77,6 +77,7 @@ pandas 0.11.1
   - ``.loc`` was not raising when passed an integer list (GH3449_)
   - Unordered time series selection was misbehaving when using label slicing (GH3448_)
   - Duplicate indexes with getitem will return items in the correct order (GH3455_, GH3457_)
+  - Duplicate indexes with and empty DataFrame.from_records will return a correct frame (GH3562_)
   - Fix sorting in a frame with a list of columns which contains datetime64[ns] dtypes (GH3461_)
   - DataFrames fetched via FRED now handle '.' as a NaN. (GH3469_)
   - Fix regression in a DataFrame apply with axis=1, objects were not being converted back
@@ -137,6 +138,7 @@ pandas 0.11.1
 .. _GH3495: https://github.com/pydata/pandas/issues/3495
 .. _GH3492: https://github.com/pydata/pandas/issues/3492
 .. _GH3552: https://github.com/pydata/pandas/issues/3552
+.. _GH3562: https://github.com/pydata/pandas/issues/3562
 .. _GH3493: https://github.com/pydata/pandas/issues/3493
 
 

pandas/core/internals.py

@@ -1960,7 +1960,8 @@ def form_blocks(arrays, names, axes):
     items = axes[0]
 
     if len(arrays) < len(items):
-        extra_items = items - Index(names)
+        nn = set(names)
+        extra_items = Index([ i for i in items if i not in nn ])
     else:
         extra_items = []
 

pandas/tests/test_frame.py

@@ -3518,6 +3518,16 @@ def test_from_records_misc_brokenness(self):
         results = df2_obj.get_dtype_counts()
         expected = Series({ 'datetime64[ns]' : 1, 'int64' : 1 })
 
+    def test_from_records_empty(self):
+        # 3562
+        result = DataFrame.from_records([], columns=['a','b','c'])
+        expected = DataFrame(columns=['a','b','c'])
+        assert_frame_equal(result, expected)
+
+        result = DataFrame.from_records([], columns=['a','b','b'])
+        expected = DataFrame(columns=['a','b','b'])
+        assert_frame_equal(result, expected)
+
     def test_to_records_floats(self):
         df = DataFrame(np.random.rand(10, 10))
         df.to_records()