narwhalified BaseMappingTransformer

CHANGELOG.rst

@@ -27,6 +27,8 @@ Changed
 - fixed issues with all null and nullable-bool column handling in dataframe_init_dispatch
 - added NaN error handling to WeightColumnMixin
 - narwhalified MeanImputer `#344 https://github.com/lvgig/tubular/issues/344_`
+- narwhalified BaseMappingTransformer `#367 <https://github.com/lvgig/tubular/issues/367>_`
+- placeholder
 - placeholder
 - placeholder
 - placeholder

tests/mapping/test_BaseMappingTransformer.py

@@ -1,5 +1,6 @@
 import re
 
+import polars as pl
 import pytest
 import test_aide as ta
 
@@ -101,13 +102,15 @@ class BaseMappingTransformerTransformTests(GenericTransformTests):
     Note this deliberately avoids starting with "Tests" so that the tests are not run on import.
     """
 
+    @pytest.mark.parametrize("library", ["pandas", "polars"])
     def test_mappings_unchanged(
         self,
         minimal_attribute_dict,
         uninitialized_transformers,
+        library,
     ):
         """Test that mappings is unchanged in transform."""
-        df = d.create_df_3()
+        df = d.create_df_3(library=library)
 
         mapping = {
             "b": {1: 2, 2: 3, 3: 4, 4: 5, 5: 6, 6: 7},
@@ -116,18 +119,17 @@ def test_mappings_unchanged(
         args = minimal_attribute_dict[self.transformer_name].copy()
         args["mappings"] = mapping
 
-        x = uninitialized_transformers[self.transformer_name](**args)
+        transformer = uninitialized_transformers[self.transformer_name](**args)
 
-        x.transform(df)
-
-        ta.equality.assert_equal_dispatch(
-            expected=mapping,
-            actual=x.mappings,
-            msg=f"{self.transformer_name}.transform has changed self.mappings unexpectedly",
-        )
+        # if transformer is not yet polars compatible, skip this test
+        if not transformer.polars_compatible and isinstance(df, pl.DataFrame):
+            return
 
+        transformer.transform(df)
 
-# Running the BaseMappingTransformerTestSuite
+        assert (
+            mapping == transformer.mappings
+        ), f"{self.transformer_name}.transform has changed self.mappings unexpectedly, expected {mapping} but got {transformer.mappings}"
 
 
 class TestInit(BaseMappingTransformerInitTests):

tubular/mapping.py

@@ -4,13 +4,18 @@
 
 import warnings
 from collections import OrderedDict
+from typing import TYPE_CHECKING
 
+import narwhals as nw
 import numpy as np
 import pandas as pd
 from pandas.api.types import is_categorical_dtype
 
 from tubular.base import BaseTransformer
 
+if TYPE_CHECKING:
+    from narwhals.typing import FrameT
+
 
 class BaseMappingTransformer(BaseTransformer):
     """Base Transformer Extension for mapping transformers.
@@ -37,7 +42,7 @@ class attribute, indicates whether transformer has been converted to polars/pand
 
     """
 
-    polars_compatible = False
+    polars_compatible = True
 
     def __init__(self, mappings: dict[str, dict], **kwargs: dict[str, bool]) -> None:
         if isinstance(mappings, dict):
@@ -60,18 +65,19 @@ def __init__(self, mappings: dict[str, dict], **kwargs: dict[str, bool]) -> None
 
         super().__init__(columns=columns, **kwargs)
 
-    def transform(self, X: pd.DataFrame) -> pd.DataFrame:
+    @nw.narwhalify
+    def transform(self, X: FrameT) -> FrameT:
         """Base mapping transformer transform method.  Checks that the mappings
         dict has been fitted and calls the BaseTransformer transform method.
 
         Parameters
         ----------
-        X : pd.DataFrame
+        X : pd/pl.DataFrame
             Data to apply mappings to.
 
         Returns
         -------
-        X : pd.DataFrame
+        X : pd/pl.DataFrame
             Input X, copied if specified by user.
 
         """