ENH: Add support for DataFrame(Categorical) (#11363)

Author: proost

doc/source/whatsnew/v1.0.0.rst

@@ -205,6 +205,7 @@ Other enhancements
   (:meth:`~DataFrame.to_parquet` / :func:`read_parquet`) using the `'pyarrow'` engine
   now preserve those data types with pyarrow >= 1.0.0 (:issue:`20612`).
 - The ``partition_cols`` argument in :meth:`DataFrame.to_parquet` now accepts a string (:issue:`27117`)
+- DataFrame constructor preserve `category` dtype with `Categorical` object (:issue:`11363`)
 
 Build Changes
 ^^^^^^^^^^^^^

pandas/core/frame.py

@@ -450,7 +450,7 @@ def __init__(
 
         # For data is list-like, or Iterable (will consume into list)
         elif isinstance(data, abc.Iterable) and not isinstance(data, (str, bytes)):
-            if not isinstance(data, abc.Sequence):
+            if not isinstance(data, (abc.Sequence, Categorical)):
                 data = list(data)
             if len(data) > 0:
                 if is_list_like(data[0]) and getattr(data[0], "ndim", 1) == 1:

pandas/tests/frame/test_constructors.py

@@ -2396,6 +2396,12 @@ class List(list):
         result = DataFrame(List([List([1, 2, 3]), List([4, 5, 6])]))
         tm.assert_frame_equal(result, expected)
 
+    def test_constructor_with_categorical(self):
+        # GH11363
+        expected = DataFrame(Series(list("aabbc"), dtype="category"))
+        result = DataFrame(Categorical(list("aabbc")))
+        tm.assert_frame_equal(result, expected)
+
 
 class TestDataFrameConstructorWithDatetimeTZ:
     def test_from_dict(self):