feat: Add methods that tell which columns would be affected by a transformer

src/safeds/data/tabular/transformation/_imputer.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import warnings
 from typing import Any
 
 import pandas as pd
@@ -178,3 +179,60 @@ def is_fitted(self) -> bool:
             Whether the transformer is fitted.
         """
         return self._wrapped_transformer is not None
+
+    def get_names_of_added_columns(self) -> list[str]:
+        """
+        Get the names of all new columns that have been added by the Imputer.
+
+        Returns
+        -------
+        added_columns : list[str]
+            A list of names of the added columns, ordered as they will appear in the table.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        warnings.warn("Imputer only changes data within columns, but does not add any columns.", stacklevel=1)
+        if not self.is_fitted():
+            raise TransformerNotFittedError
+        return []
+
+    # (Must implement abstract method, cannot instantiate class otherwise.)
+    def get_names_of_changed_columns(self) -> list[str]:
+        """
+         Get the names of all columns that may have been changed by the Imputer.
+
+        Returns
+        -------
+        changed_columns : list[str]
+             The list of (potentially) changed column names, as passed to fit.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        if self._column_names is None:
+            raise TransformerNotFittedError
+        return self._column_names
+
+    def get_names_of_removed_columns(self) -> list[str]:
+        """
+        Get the names of all columns that have been removed by the Imputer.
+
+        Returns
+        -------
+        removed_columns : list[str]
+            A list of names of the removed columns, ordered as they appear in the table the Imputer was fitted on.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        warnings.warn("Imputer only changes data within columns, but does not remove any columns.", stacklevel=1)
+        if not self.is_fitted():
+            raise TransformerNotFittedError
+        return []

src/safeds/data/tabular/transformation/_label_encoder.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import warnings
+
 from sklearn.preprocessing import OrdinalEncoder as sk_OrdinalEncoder
 
 from safeds.data.tabular.containers import Table
@@ -126,3 +128,60 @@ def is_fitted(self) -> bool:
             Whether the transformer is fitted.
         """
         return self._wrapped_transformer is not None
+
+    def get_names_of_added_columns(self) -> list[str]:
+        """
+        Get the names of all new columns that have been added by the LabelEncoder.
+
+        Returns
+        -------
+        added_columns : list[str]
+            A list of names of the added columns, ordered as they will appear in the table.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        warnings.warn("LabelEncoder only changes data within columns, but does not add any columns.", stacklevel=1)
+        if not self.is_fitted():
+            raise TransformerNotFittedError
+        return []
+
+    # (Must implement abstract method, cannot instantiate class otherwise.)
+    def get_names_of_changed_columns(self) -> list[str]:
+        """
+         Get the names of all columns that may have been changed by the LabelEncoder.
+
+        Returns
+        -------
+        changed_columns : list[str]
+             The list of (potentially) changed column names, as passed to fit.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        if self._column_names is None:
+            raise TransformerNotFittedError
+        return self._column_names
+
+    def get_names_of_removed_columns(self) -> list[str]:
+        """
+        Get the names of all columns that have been removed by the LabelEncoder.
+
+        Returns
+        -------
+        removed_columns : list[str]
+            A list of names of the removed columns, ordered as they appear in the table the LabelEncoder was fitted on.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        warnings.warn("LabelEncoder only changes data within columns, but does not remove any columns.", stacklevel=1)
+        if not self.is_fitted():
+            raise TransformerNotFittedError
+        return []

src/safeds/data/tabular/transformation/_one_hot_encoder.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import warnings
 from collections import Counter
 from typing import Any
 
@@ -249,3 +250,59 @@ def is_fitted(self) -> bool:
             Whether the transformer is fitted.
         """
         return self._column_names is not None and self._value_to_column is not None
+
+    def get_names_of_added_columns(self) -> list[str]:
+        """
+        Get the names of all new columns that have been added by the OneHotEncoder.
+
+        Returns
+        -------
+        added_columns : list[str]
+            A list of names of the added columns, ordered as they will appear in the table.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        if self._column_names is None:
+            raise TransformerNotFittedError
+        return [name for column_names in self._column_names.values() for name in column_names]
+
+    # (Must implement abstract method, cannot instantiate class otherwise.)
+    def get_names_of_changed_columns(self) -> list[str]:
+        """
+         Get the names of all columns that have been changed by the OneHotEncoder (none).
+
+        Returns
+        -------
+        changed_columns : list[str]
+             The empty list.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        warnings.warn("OneHotEncoder only removes and adds, but does not change any columns.", stacklevel=1)
+        if not self.is_fitted():
+            raise TransformerNotFittedError
+        return []
+
+    def get_names_of_removed_columns(self) -> list[str]:
+        """
+        Get the names of all columns that have been removed by the OneHotEncoder.
+
+        Returns
+        -------
+        removed_columns : list[str]
+            A list of names of the removed columns, ordered as they appear in the table the OneHotEncoder was fitted on.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+        if self._column_names is None:
+            raise TransformerNotFittedError
+        return list(self._column_names.keys())

src/safeds/data/tabular/transformation/_table_transformer.py

@@ -53,6 +53,54 @@ def transform(self, table: Table) -> Table:
             If the transformer has not been fitted yet.
         """
 
+    @abstractmethod
+    def get_names_of_added_columns(self) -> list[str]:
+        """
+        Get the names of all new columns that have been added by the transformer.
+
+        Returns
+        -------
+        added_columns : list[str]
+            A list of names of the added columns, ordered as they will appear in the table.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+
+    @abstractmethod
+    def get_names_of_changed_columns(self) -> list[str]:
+        """
+         Get the names of all columns that have been changed by the transformer.
+
+        Returns
+        -------
+        changed_columns : list[str]
+             A list of names of changed columns, ordered as they appear in the table.
+
+        Raises
+        ------
+         TransformerNotFittedError
+             If the transformer has not been fitted yet.
+        """
+
+    @abstractmethod
+    def get_names_of_removed_columns(self) -> list[str]:
+        """
+        Get the names of all columns that have been removed by the transformer.
+
+        Returns
+        -------
+        removed_columns : list[str]
+            A list of names of the removed columns, ordered as they appear in the table the transformer was fitted on.
+
+        Raises
+        ------
+        TransformerNotFittedError
+            If the transformer has not been fitted yet.
+        """
+
     @abstractmethod
     def is_fitted(self) -> bool:
         """

tests/safeds/data/tabular/transformation/test_imputer.py

@@ -207,3 +207,55 @@ def test_should_not_change_original_table(self) -> None:
         )
 
         assert table == expected
+
+    def test_get_names_of_added_columns(self) -> None:
+        transformer = Imputer(strategy=Imputer.Strategy.Constant(1))
+        with pytest.warns(
+            UserWarning,
+            match="Imputer only changes data within columns, but does not add any columns.",
+        ), pytest.raises(TransformerNotFittedError):
+            transformer.get_names_of_added_columns()
+
+        table = Table(
+            {
+                "a": [1, None],
+                "b": [1, 1],
+            },
+        )
+        transformer = transformer.fit(table, None)
+        with pytest.warns(UserWarning, match="Imputer only changes data within columns, but does not add any columns."):
+            assert transformer.get_names_of_added_columns() == []
+
+    def test_get_names_of_changed_columns(self) -> None:
+        transformer = Imputer(strategy=Imputer.Strategy.Constant(1))
+        with pytest.raises(TransformerNotFittedError):
+            transformer.get_names_of_changed_columns()
+        table = Table(
+            {
+                "a": [1, None],
+                "b": [1, 1],
+            },
+        )
+        transformer = transformer.fit(table, None)
+        assert transformer.get_names_of_changed_columns() == ["a", "b"]
+
+    def test_get_names_of_removed_columns(self) -> None:
+        transformer = Imputer(strategy=Imputer.Strategy.Constant(1))
+        with pytest.warns(
+            UserWarning,
+            match="Imputer only changes data within columns, but does not remove any columns.",
+        ), pytest.raises(TransformerNotFittedError):
+            transformer.get_names_of_removed_columns()
+
+        table = Table(
+            {
+                "a": [1, None],
+                "b": [1, 1],
+            },
+        )
+        transformer = transformer.fit(table, None)
+        with pytest.warns(
+            UserWarning,
+            match="Imputer only changes data within columns, but does not remove any columns.",
+        ):
+            assert transformer.get_names_of_removed_columns() == []

tests/safeds/data/tabular/transformation/test_label_encoder.py

@@ -137,6 +137,58 @@ def test_should_not_change_original_table(self) -> None:
 
         assert table == expected
 
+    def test_get_names_of_added_columns(self) -> None:
+        transformer = LabelEncoder()
+        with pytest.warns(
+            UserWarning,
+            match="LabelEncoder only changes data within columns, but does not add any columns.",
+        ), pytest.raises(TransformerNotFittedError):
+            transformer.get_names_of_added_columns()
+
+        table = Table(
+            {
+                "a": ["b"],
+            },
+        )
+        transformer = transformer.fit(table, None)
+        with pytest.warns(
+            UserWarning,
+            match="LabelEncoder only changes data within columns, but does not add any columns.",
+        ):
+            assert transformer.get_names_of_added_columns() == []
+
+    def test_get_names_of_changed_columns(self) -> None:
+        transformer = LabelEncoder()
+        with pytest.raises(TransformerNotFittedError):
+            transformer.get_names_of_changed_columns()
+        table = Table(
+            {
+                "a": ["b"],
+            },
+        )
+        transformer = transformer.fit(table, None)
+        assert transformer.get_names_of_changed_columns() == ["a"]
+
+    def test_get_names_of_removed_columns(self) -> None:
+        transformer = LabelEncoder()
+        with pytest.warns(
+            UserWarning,
+            match="LabelEncoder only changes data within columns, but does not remove any columns.",
+        ), pytest.raises(TransformerNotFittedError):
+            transformer.get_names_of_removed_columns()
+
+        table = Table(
+            {
+                "a": ["b"],
+            },
+        )
+        transformer = transformer.fit(table, None)
+        with pytest.warns(
+            UserWarning,
+            match="LabelEncoder only changes data within columns, but does not remove any columns.",
+        ):
+            assert transformer.get_names_of_removed_columns() == []
+
 
 class TestInverseTransform:
     @pytest.mark.parametrize(