Update fill_nan_with_none to not raise Pandas FutureWarning (#1024)

Author: R-Palazzo

rdt/transformers/utils.py

@@ -175,6 +175,17 @@ def strings_from_regex(regex, max_repeat=16):
     return _from_generators(generators, max_repeat), np.prod(sizes, dtype=np.complex128).real
 
 
+def _fill_nan_with_none_series(data):
+    sentinel = object()
+    dtype = data.dtype
+    if isinstance(dtype, pd.CategoricalDtype):
+        data = data.cat.add_categories([sentinel])
+        data = data.fillna(sentinel).replace({sentinel: None})
+        return pd.Series(pd.Categorical(data, categories=dtype.categories), index=data.index)
+
+    return data.fillna(sentinel).replace({sentinel: None})
+
+
 def fill_nan_with_none(data):
     """Replace all nan values with None.
 
@@ -185,7 +196,10 @@ def fill_nan_with_none(data):
         data:
             Original data with nan values replaced by None.
     """
-    return data.infer_objects().fillna(np.nan).replace([np.nan], [None])
+    if isinstance(data, pd.DataFrame):
+        return data.apply(_fill_nan_with_none_series)
+
+    return _fill_nan_with_none_series(data)
 
 
 def flatten_column_list(column_list):

tests/unit/transformers/test_utils.py

@@ -16,6 +16,7 @@
     _any,
     _cast_to_type,
     _extract_timezone_from_a_string,
+    _fill_nan_with_none_series,
     _get_utc_offset,
     _handle_enforce_uniqueness_and_cardinality_rule,
     _max_repeat,
@@ -167,6 +168,45 @@ def test_fill_nan_with_none_no_warning():
     pd.testing.assert_series_equal(result, expected)
 
 
+def test__fill_nan_with_none_series():
+    """Test the ``_fill_nan_with_none_series`` method."""
+    # Setup
+    series = pd.Series([1.0, 2.0, 3.0, np.nan], dtype='object')
+    categorical_serie = pd.Series(['a', 'b', 'c', 'd', np.nan], dtype='category')
+
+    # Run
+    result = _fill_nan_with_none_series(series)
+    result_categorical = _fill_nan_with_none_series(categorical_serie)
+
+    # Assert
+    expected_result = pd.Series([1.0, 2.0, 3.0, None], dtype='object')
+    pd.testing.assert_series_equal(result, expected_result)
+    expected_result_categorical = pd.Series(
+        pd.Categorical(['a', 'b', 'c', 'd', None], categories=['a', 'b', 'c', 'd'])
+    )
+    pd.testing.assert_series_equal(result_categorical, expected_result_categorical)
+
+
+def test_fill_nan_with_none_series():
+    """Test the `fill_nan_with_none_series` function."""
+    # Setup
+    series = pd.Series([1.0, 2.0, 3.0, np.nan], dtype='object')
+    data = pd.DataFrame({'col1': series})
+    data_2 = pd.DataFrame({'col1': series, 'col2': ['a', 'b', 'c', np.nan]})
+
+    # Run
+    result_series = _fill_nan_with_none_series(series)
+    result_data = fill_nan_with_none(data)
+    result_data_2 = fill_nan_with_none(data_2)
+
+    # Assert
+    expected_result = pd.Series([1.0, 2.0, 3.0, None], dtype='object')
+    expected_result_data_2 = pd.DataFrame({'col1': expected_result, 'col2': ['a', 'b', 'c', None]})
+    pd.testing.assert_series_equal(result_series, expected_result)
+    pd.testing.assert_frame_equal(result_data, pd.DataFrame({'col1': expected_result}))
+    pd.testing.assert_frame_equal(result_data_2, expected_result_data_2)
+
+
 def test_check_nan_in_transform():
     """Test ``check_nan_in_transform`` method.