feat: add KNearestNeighborsImputer

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

@@ -2,8 +2,6 @@
 
 from typing import TYPE_CHECKING
 
-from numpy import nan
-
 from safeds._utils import _structural_hash
 from safeds._validation import _check_bounds, _check_columns_exist, _ClosedBound
 from safeds.data.tabular.containers import Table
@@ -38,15 +36,15 @@ def __init__(
         neighbor_count: int,
         *,
         column_names: str | list[str] | None = None,
-        value_to_replace: float | str | None = nan,
+        value_to_replace: float | str | None = None,
     ) -> None:
         super().__init__(column_names)
 
         _check_bounds(name="neighbor_count", actual=neighbor_count, lower_bound=_ClosedBound(1))
 
         # parameter
         self._neighbor_count: int = neighbor_count
-        self._value_to_replace: float | str | None = value_to_replace if value_to_replace is not None else nan
+        self._value_to_replace: float | str | None = value_to_replace
 
         # attributes
         self._wrapped_transformer: sk_KNNImputer | None = None
@@ -73,6 +71,10 @@ def neighbor_count(self) -> int:
         """The number of neighbors to consider when imputing missing values."""
         return self._neighbor_count
 
+    @property
+    def value_to_replace(self) -> float | str | None:
+        """The value to replace."""
+        return self._value_to_replace
     # ------------------------------------------------------------------------------------------------------------------
     # Learning and transformation
     # ------------------------------------------------------------------------------------------------------------------
@@ -108,6 +110,10 @@ def fit(self, table: Table) -> KNearestNeighborsImputer:
         else:
             column_names = self._column_names
             _check_columns_exist(table, column_names)
+
+        if self._value_to_replace is None:
+            from numpy import nan
+            self._value_to_replace = nan
 
         wrapped_transformer = sk_KNNImputer(n_neighbors=self._neighbor_count, missing_values=self._value_to_replace)
         wrapped_transformer.set_output(transform="polars")

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

@@ -17,6 +17,14 @@ def test_neighbor_count(self) -> None:
         knn = KNearestNeighborsImputer(neighbor_count=5)
         assert knn.neighbor_count == 5
 
+    def test_value_to_replace_none(self)->None:
+        knn = KNearestNeighborsImputer(neighbor_count=5)
+        assert knn.value_to_replace is None
+
+    def test_value_to_replace_number(self)->None:
+        knn = KNearestNeighborsImputer(neighbor_count=5, value_to_replace=1)
+        assert knn.value_to_replace == 1
+
 
 class TestFit:
     def test_should_raise_if_column_not_found(self) -> None: