BUG: DataFrame(nested_object_ndarray) match DataFrame(nested_pandas_array) (#45040)

Author: jbrockmendel

doc/source/whatsnew/v1.4.0.rst

@@ -669,6 +669,7 @@ Conversion
 ^^^^^^^^^^
 - Bug in :class:`UInt64Index` constructor when passing a list containing both positive integers small enough to cast to int64 and integers too large too hold in int64 (:issue:`42201`)
 - Bug in :class:`Series` constructor returning 0 for missing values with dtype ``int64`` and ``False`` for dtype ``bool`` (:issue:`43017`, :issue:`43018`)
+- Bug in constructing a :class:`DataFrame` from a :class:`PandasArray` containing :class:`Series` objects behaving differently than an equivalent ``np.ndarray`` (:issue:`43986`)
 - Bug in :class:`IntegerDtype` not allowing coercion from string dtype (:issue:`25472`)
 - Bug in :func:`to_datetime` with ``arg:xr.DataArray`` and ``unit="ns"`` specified raises TypeError (:issue:`44053`)
 - Bug in :meth:`DataFrame.convert_dtypes` not returning the correct type when a subclass does not overload :meth:`_constructor_sliced` (:issue:`43201`)

pandas/core/apply.py

@@ -57,7 +57,6 @@
 )
 import pandas.core.common as com
 from pandas.core.construction import (
-    array as pd_array,
     create_series_with_explicit_dtype,
     ensure_wrapped_if_datetimelike,
 )
@@ -1142,9 +1141,9 @@ def apply_standard(self) -> DataFrame | Series:
                 )
 
         if len(mapped) and isinstance(mapped[0], ABCSeries):
-            # GH 25959 use pd.array instead of tolist
-            # so extension arrays can be used
-            return obj._constructor_expanddim(pd_array(mapped), index=obj.index)
+            # GH#43986 Need to do list(mapped) in order to get treated as nested
+            #  See also GH#25959 regarding EA support
+            return obj._constructor_expanddim(list(mapped), index=obj.index)
         else:
             return obj._constructor(mapped, index=obj.index).__finalize__(
                 obj, method="apply"

pandas/core/frame.py

@@ -666,7 +666,7 @@ def __init__(
                     typ=manager,
                 )
 
-        elif isinstance(data, (np.ndarray, Series, Index)):
+        elif isinstance(data, (np.ndarray, Series, Index, ExtensionArray)):
             if data.dtype.names:
                 # i.e. numpy structured array
                 data = cast(np.ndarray, data)

pandas/tests/frame/test_constructors.py

@@ -1305,6 +1305,20 @@ def test_constructor_list_of_lists(self):
         result = DataFrame(data)
         tm.assert_frame_equal(result, expected)
 
+    def test_nested_pandasarray_matches_nested_ndarray(self):
+        # GH#43986
+        ser = Series([1, 2])
+
+        arr = np.array([None, None], dtype=object)
+        arr[0] = ser
+        arr[1] = ser * 2
+
+        df = DataFrame(arr)
+        expected = DataFrame(pd.array(arr))
+        tm.assert_frame_equal(df, expected)
+        assert df.shape == (2, 1)
+        tm.assert_numpy_array_equal(df[0].values, arr)
+
     def test_constructor_list_like_data_nested_list_column(self):
         # GH 32173
         arrays = [list("abcd"), list("cdef")]