feat: usable constructor for TaggedTable (#299)

Closes #293.

### Summary of Changes

Change constructor of `TaggedTable` to be more usable. The usual way to
get a `TaggedTable` is still to call the `tag_column` method of `Table`.

---------

Co-authored-by: megalinter-bot <[email protected]>

src/safeds/data/tabular/containers/_table.py

@@ -51,6 +51,21 @@ class Table:
     | [from_dict][safeds.data.tabular.containers._table.Table.from_dict]           | Create a table from a dictionary.      |
     | [from_columns][safeds.data.tabular.containers._table.Table.from_columns]     | Create a table from a list of columns. |
     | [from_rows][safeds.data.tabular.containers._table.Table.from_rows]           | Create a table from a list of rows.    |
+
+    Parameters
+    ----------
+    data : Mapping[str, Sequence[Any]] | None
+        The data. If None, an empty table is created.
+
+    Raises
+    ------
+    ColumnLengthMismatchError
+        If columns have different lengths.
+
+    Examples
+    --------
+    >>> from safeds.data.tabular.containers import Table
+    >>> table = Table({"a": [1, 2, 3], "b": [4, 5, 6]})
     """
 
     # ------------------------------------------------------------------------------------------------------------------
@@ -62,8 +77,6 @@ def from_csv_file(path: str | Path) -> Table:
         """
         Read data from a CSV file into a table.
 
-        This table is not modified.
-
         Parameters
         ----------
         path : str | Path
@@ -91,8 +104,6 @@ def from_excel_file(path: str | Path) -> Table:
         """
         Read data from an Excel file into a table.
 
-        This table is not modified.
-
         Parameters
         ----------
         path : str | Path
@@ -122,8 +133,6 @@ def from_json_file(path: str | Path) -> Table:
         """
         Read data from a JSON file into a table.
 
-        This table is not modified.
-
         Parameters
         ----------
         path : str | Path
@@ -151,8 +160,6 @@ def from_dict(data: dict[str, list[Any]]) -> Table:
         """
         Create a table from a dictionary that maps column names to column values.
 
-        This table is not modified.
-
         Parameters
         ----------
         data : dict[str, list[Any]]
@@ -175,8 +182,6 @@ def from_columns(columns: list[Column]) -> Table:
         """
         Return a table created from a list of columns.
 
-        This table is not modified.
-
         Parameters
         ----------
         columns : list[Column]
@@ -208,8 +213,6 @@ def from_rows(rows: list[Row]) -> Table:
         """
         Return a table created from a list of rows.
 
-        This table is not modified.
-
         Parameters
         ----------
         rows : list[Row]
@@ -245,8 +248,6 @@ def _from_pandas_dataframe(data: pd.DataFrame, schema: Schema | None = None) ->
         """
         Create a table from a `pandas.DataFrame`.
 
-        This table is not modified.
-
         Parameters
         ----------
         data : pd.DataFrame
@@ -1070,7 +1071,7 @@ def tag_columns(self, target_name: str, feature_names: list[str] | None = None)
         ----------
         target_name : str
             Name of the target column.
-        feature_names : Optional[list[str]]
+        feature_names : list[str] | None
             Names of the feature columns. If None, all columns except the target column are used.
 
         Returns
@@ -1080,7 +1081,7 @@ def tag_columns(self, target_name: str, feature_names: list[str] | None = None)
         """
         from ._tagged_table import TaggedTable
 
-        return TaggedTable(self._data, self._schema, target_name, feature_names)
+        return TaggedTable._from_table(self, target_name, feature_names)
 
     def transform_column(self, name: str, transformer: Callable[[Row], Any]) -> Table:
         """

src/safeds/data/tabular/containers/_tagged_table.py

@@ -1,7 +1,12 @@
-import pandas as pd
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
 
 from safeds.data.tabular.containers import Column, Table
-from safeds.data.tabular.typing import Schema
+
+if TYPE_CHECKING:
+    from collections.abc import Mapping, Sequence
+    from typing import Any
 
 
 class TaggedTable(Table):
@@ -10,30 +15,128 @@ class TaggedTable(Table):
 
     Parameters
     ----------
-    data : Iterable
+    data : Mapping[str, Sequence[Any]]
         The data.
     target_name : str
         Name of the target column.
-    feature_names : Optional[list[str]]
+    feature_names : list[str] | None
         Names of the feature columns. If None, all columns except the target column are used.
-    schema : Optional[Schema]
-        The schema of the table. If not specified, the schema will be inferred from the data.
+
+    Raises
+    ------
+    ColumnLengthMismatchError
+        If columns have different lengths.
+    ValueError
+        If the target column is also a feature column.
+    ValueError
+        If no feature columns are specified.
+
+    Examples
+    --------
+    >>> from safeds.data.tabular.containers import Table, TaggedTable
+    >>> table = Table({"col1": ["a", "b"], "col2": [1, 2]})
+    >>> tagged_table = table.tag_columns("col2", ["col1"])
     """
 
+    # ------------------------------------------------------------------------------------------------------------------
+    # Creation
+    # ------------------------------------------------------------------------------------------------------------------
+
+    @staticmethod
+    def _from_table(
+        table: Table,
+        target_name: str,
+        feature_names: list[str] | None = None,
+    ) -> TaggedTable:
+        """
+        Create a tagged table from a table.
+
+        Parameters
+        ----------
+        table : Table
+            The table.
+        target_name : str
+            Name of the target column.
+        feature_names : list[str] | None
+            Names of the feature columns. If None, all columns except the target column are used.
+
+        Returns
+        -------
+        tagged_table : TaggedTable
+            The created table.
+
+        Raises
+        ------
+        ValueError
+            If the target column is also a feature column.
+        ValueError
+            If no feature columns are specified.
+
+        Examples
+        --------
+        >>> from safeds.data.tabular.containers import Table, TaggedTable
+        >>> table = Table({"col1": ["a", "b", "c", "a"], "col2": [1, 2, 3, 4]})
+        >>> tagged_table = TaggedTable._from_table(table, "col2", ["col1"])
+        """
+        # If no feature names are specified, use all columns except the target column
+        if feature_names is None:
+            feature_names = table.column_names
+            if target_name in feature_names:
+                feature_names.remove(target_name)
+
+        # Validate inputs
+        if target_name in feature_names:
+            raise ValueError(f"Column '{target_name}' cannot be both feature and target.")
+        if len(feature_names) == 0:
+            raise ValueError("At least one feature column must be specified.")
+
+        # Create result
+        result = object.__new__(TaggedTable)
+
+        result._data = table._data
+        result._schema = table.schema
+        result._features = result.keep_only_columns(feature_names)
+        result._target = result.get_column(target_name)
+
+        return result
+
     # ------------------------------------------------------------------------------------------------------------------
     # Dunder methods
     # ------------------------------------------------------------------------------------------------------------------
 
-    # noinspection PyMissingConstructor
     def __init__(
         self,
-        data: pd.DataFrame,
-        schema: Schema,
+        data: Mapping[str, Sequence[Any]],
         target_name: str,
         feature_names: list[str] | None = None,
     ):
-        self._data = data
-        self._schema = schema
+        """
+        Create a tagged table from a mapping of column names to their values.
+
+        Parameters
+        ----------
+        data : Mapping[str, Sequence[Any]]
+            The data.
+        target_name : str
+            Name of the target column.
+        feature_names : list[str] | None
+            Names of the feature columns. If None, all columns except the target column are used.
+
+        Raises
+        ------
+        ColumnLengthMismatchError
+            If columns have different lengths.
+        ValueError
+            If the target column is also a feature column.
+        ValueError
+            If no feature columns are specified.
+
+        Examples
+        --------
+        >>> from safeds.data.tabular.containers import TaggedTable
+        >>> table = TaggedTable({"a": [1, 2, 3], "b": [4, 5, 6]}, "b", ["a"])
+        """
+        super().__init__(data)
 
         # If no feature names are specified, use all columns except the target column
         if feature_names is None:

tests/safeds/data/tabular/containers/test_tagged_table.py

@@ -4,44 +4,71 @@
 
 
 @pytest.fixture()
-def table() -> Table:
-    return Table(
-        {
-            "A": [1, 4],
-            "B": [2, 5],
-            "C": [3, 6],
-            "T": [0, 1],
-        },
-    )
+def data() -> dict[str, list[int]]:
+    return {
+        "A": [1, 4],
+        "B": [2, 5],
+        "C": [3, 6],
+        "T": [0, 1],
+    }
+
+
+@pytest.fixture()
+def table(data: dict[str, list[int]]) -> Table:
+    return Table(data)
 
 
 @pytest.fixture()
 def tagged_table(table: Table) -> TaggedTable:
     return table.tag_columns(target_name="T")
 
 
-class TestInit:
+class TestFromTable:
     def test_should_raise_if_a_feature_does_not_exist(self, table: Table) -> None:
         with pytest.raises(UnknownColumnNameError):
-            table.tag_columns(target_name="T", feature_names=["A", "B", "C", "D"])
+            TaggedTable._from_table(table, target_name="T", feature_names=["A", "B", "C", "D"])
 
     def test_should_raise_if_target_does_not_exist(self, table: Table) -> None:
         with pytest.raises(UnknownColumnNameError):
-            table.tag_columns(target_name="D")
+            TaggedTable._from_table(table, target_name="D")
 
     def test_should_raise_if_features_and_target_overlap(self, table: Table) -> None:
         with pytest.raises(ValueError, match="Column 'A' cannot be both feature and target."):
-            table.tag_columns(target_name="A", feature_names=["A", "B", "C"])
+            TaggedTable._from_table(table, target_name="A", feature_names=["A", "B", "C"])
 
     def test_should_raise_if_features_are_empty_explicitly(self, table: Table) -> None:
         with pytest.raises(ValueError, match="At least one feature column must be specified."):
-            table.tag_columns(target_name="A", feature_names=[])
+            TaggedTable._from_table(table, target_name="A", feature_names=[])
 
-    def test_should_raise_if_features_are_empty_implicitly(self, table: Table) -> None:
+    def test_should_raise_if_features_are_empty_implicitly(self) -> None:
         table = Table({"A": [1, 4]})
 
         with pytest.raises(ValueError, match="At least one feature column must be specified."):
-            table.tag_columns(target_name="A")
+            TaggedTable._from_table(table, target_name="A")
+
+
+class TestInit:
+    def test_should_raise_if_a_feature_does_not_exist(self, data: dict[str, list[int]]) -> None:
+        with pytest.raises(UnknownColumnNameError):
+            TaggedTable(data, target_name="T", feature_names=["A", "B", "C", "D"])
+
+    def test_should_raise_if_target_does_not_exist(self, data: dict[str, list[int]]) -> None:
+        with pytest.raises(UnknownColumnNameError):
+            TaggedTable(data, target_name="D")
+
+    def test_should_raise_if_features_and_target_overlap(self, data: dict[str, list[int]]) -> None:
+        with pytest.raises(ValueError, match="Column 'A' cannot be both feature and target."):
+            TaggedTable(data, target_name="A", feature_names=["A", "B", "C"])
+
+    def test_should_raise_if_features_are_empty_explicitly(self, data: dict[str, list[int]]) -> None:
+        with pytest.raises(ValueError, match="At least one feature column must be specified."):
+            TaggedTable(data, target_name="A", feature_names=[])
+
+    def test_should_raise_if_features_are_empty_implicitly(self) -> None:
+        data = {"A": [1, 4]}
+
+        with pytest.raises(ValueError, match="At least one feature column must be specified."):
+            TaggedTable(data, target_name="A")
 
 
 class TestFeatures: