BUG: Duplicated returns boolean dataframe (#25234)

Author: Sterling Paramore

doc/source/whatsnew/v0.24.2.rst

@@ -24,6 +24,8 @@ Fixed Regressions
 - Fixed issue in ``DataFrame`` construction with passing a mixed list of mixed types could segfault. (:issue:`25075`)
 - Fixed regression in :meth:`DataFrame.apply` causing ``RecursionError`` when ``dict``-like classes were passed as argument. (:issue:`25196`)
 
+- Fixed regression in :meth:`DataFrame.duplicated()`, where empty dataframe was not returning a boolean dtyped Series. (:issue:`25184`)
+
 .. _whatsnew_0242.enhancements:
 
 Enhancements

doc/source/whatsnew/v0.25.0.rst

@@ -68,6 +68,8 @@ Performance Improvements
 Bug Fixes
 ~~~~~~~~~
 
+-
+
 Categorical
 ^^^^^^^^^^^
 

pandas/core/frame.py

@@ -4619,7 +4619,7 @@ def duplicated(self, subset=None, keep='first'):
  from pandas._libs.hashtable import duplicated_int64, _SIZE_HINT_LIMIT
 
  if self.empty:
- return Series()
+ return Series(dtype=bool)
 
  def f(vals):
  labels, shape = algorithms.factorize(

pandas/tests/frame/test_duplicates.py

@@ -182,6 +182,17 @@ def test_drop_duplicates():
  assert df.duplicated(keep=keep).sum() == 0
 
 
+def test_duplicated_on_empty_frame():
+ # GH 25184
+
+ df = DataFrame(columns=['a', 'b'])
+ dupes = df.duplicated('a')
+
+ result = df[dupes]
+ expected = df.copy()
+ tm.assert_frame_equal(result, expected)
+
+
 def test_drop_duplicates_with_duplicate_column_names():
  # GH17836
  df = DataFrame([