BUG/API: _values_for_factorize/_from_factorized round-trip

Author: jbrockmendel

pandas/core/arrays/boolean.py

@@ -320,7 +320,8 @@ def _values_for_factorize(self) -> Tuple[np.ndarray, int]:
 
     @classmethod
     def _from_factorized(cls, values, original: "BooleanArray") -> "BooleanArray":
-        return cls._from_sequence(values, dtype=original.dtype)
+        mask = values == -1
+        return cls(values.astype(bool), mask)
 
     _HANDLED_TYPES = (np.ndarray, numbers.Number, bool, np.bool_)
 

pandas/tests/extension/base/reshaping.py

@@ -324,3 +324,10 @@ def test_transpose(self, data):
         self.assert_frame_equal(result, expected)
         self.assert_frame_equal(np.transpose(np.transpose(df)), df)
         self.assert_frame_equal(np.transpose(np.transpose(df[["A"]])), df[["A"]])
+
+    def test_factorize_roundtrip(self, data):
+        # GH#32673
+        values = data._values_for_factorize()[0]
+        result = type(data)._from_factorized(values, data)
+
+        self.assert_equal(result, data)

pandas/tests/extension/json/array.py

@@ -65,7 +65,9 @@ def _from_sequence(cls, scalars, dtype=None, copy=False):
 
     @classmethod
     def _from_factorized(cls, values, original):
-        return cls([UserDict(x) for x in values if x != ()])
+        return cls(
+            [UserDict(x) if x != () else original.dtype.na_value for x in values]
+        )
 
     def __getitem__(self, item):
         if isinstance(item, numbers.Integral):

pandas/tests/extension/test_datetime.py

@@ -4,6 +4,7 @@
 from pandas.core.dtypes.dtypes import DatetimeTZDtype
 
 import pandas as pd
+import pandas._testing as tm
 from pandas.core.arrays import DatetimeArray
 from pandas.tests.extension import base
 
@@ -201,6 +202,13 @@ def test_unstack(self, obj):
         result = ser.unstack(0)
         self.assert_equal(result, expected)
 
+    def test_factorize_roundtrip(self, data):
+        # GH#32673, for DTA we dont preserve freq
+        values = data._values_for_factorize()[0]
+        result = type(data)._from_factorized(values, data)
+
+        tm.assert_numpy_array_equal(result.asi8, data.asi8)
+
 
 class TestSetitem(BaseDatetimeTests, base.BaseSetitemTests):
     pass