feat: get first cell with value other than None (#904)

Closes #799 

### Summary of Changes

Added static method to Cell, which returns a Cell containing the polars
expression of the first Cell in the list that is not None.
Works on a list of Cells, regardless of Cell type (numeric, string,
date, etc.).
Returns None if given an empty list.

---------

Co-authored-by: Saman Hushi <saman@hushalsadat.com>
Co-authored-by: Lars Reimann <mail@larsreimann.com>
Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

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

@@ -21,6 +21,32 @@ class Cell(ABC, Generic[T_co]):
     This class cannot be instantiated directly. It is only used for arguments of callbacks.
     """
 
+    # ------------------------------------------------------------------------------------------------------------------
+    # Static methods
+    # ------------------------------------------------------------------------------------------------------------------
+
+    @staticmethod
+    def first_not_none(cells: list[Cell]) -> Cell:
+        """
+        Return the first cell from the given list that is not None.
+
+        Parameters
+        ----------
+        cells:
+            The list of cells to be searched.
+
+        Returns
+        -------
+        cell:
+            Returns the contents of the first cell that is not None.
+            If all cells in the list are None or the list is empty returns None.
+        """
+        import polars as pl
+
+        from ._lazy_cell import _LazyCell  # circular import
+
+        return _LazyCell(pl.coalesce([cell._polars_expression for cell in cells]))
+
     # ------------------------------------------------------------------------------------------------------------------
     # Dunder methods
     # ------------------------------------------------------------------------------------------------------------------

tests/safeds/data/tabular/containers/_cell/test_first_not_none.py

@@ -0,0 +1,57 @@
+from datetime import date, time
+
+import polars as pl
+import pytest
+from safeds.data.tabular.containers._cell import Cell
+from safeds.data.tabular.containers._lazy_cell import _LazyCell
+
+
+class TestFirstNotNone:
+    def test_should_return_none(self) -> None:
+        to_eval: list[Cell] = [_LazyCell(None) for i in range(5)]
+        res = Cell.first_not_none(to_eval)
+        assert res.eq(_LazyCell(None))
+
+    @pytest.mark.parametrize(
+        ("list_of_cells", "expected"),
+        [
+            ([_LazyCell(None), _LazyCell(1), _LazyCell(None), _LazyCell(4)], _LazyCell(1)),
+            ([_LazyCell(i) for i in range(5)], _LazyCell(1)),
+            (
+                [
+                    _LazyCell(None),
+                    _LazyCell(None),
+                    _LazyCell(pl.lit("Hello, World!")),
+                    _LazyCell(pl.lit("Not returned")),
+                ],
+                _LazyCell("Hello, World!"),
+            ),
+            ([_LazyCell(pl.lit(i)) for i in ["a", "b", "c", "d"]], _LazyCell(pl.lit("a"))),
+            ([_LazyCell(i) for i in [None, time(0, 0, 0, 0), None, time(1, 1, 1, 1)]], _LazyCell(time(0, 0, 0, 0))),
+            (
+                [_LazyCell(i) for i in [time(0, 0, 0, 0), time(1, 1, 1, 1), time(2, 2, 2, 2), time(3, 3, 3, 3)]],
+                _LazyCell(time(0, 0, 0, 0)),
+            ),
+            ([_LazyCell(i) for i in [None, date(2000, 1, 1), date(1098, 3, 4), None]], _LazyCell(date(2000, 1, 1))),
+            ([_LazyCell(date(2000, 3, i)) for i in range(1, 5)], _LazyCell(date(2000, 3, 1))),
+            ([_LazyCell(i) for i in [None, pl.lit("a"), 1, time(0, 0, 0, 0)]], _LazyCell(pl.lit("a"))),
+            ([_LazyCell(i) for i in [time(1, 1, 1, 1), 0, pl.lit("c"), date(2020, 1, 7)]], _LazyCell(time(1, 1, 1, 1))),
+            ([], _LazyCell(None)),
+        ],
+        ids=[
+            "numeric_with_null",
+            "numeric_no_null",
+            "strings_with_null",
+            "strings_no_null",
+            "times_with_null",
+            "times_no_null",
+            "dates_with_null",
+            "dates_no_null",
+            "mixed_with_null",
+            "mixed_no_null",
+            "empty_list",
+        ],
+    )
+    def test_should_return_first_non_none_value(self, list_of_cells: list[Cell], expected: Cell) -> None:
+        res = Cell.first_not_none(list_of_cells)
+        assert res.eq(expected)