feat: Tolerances for inner lists and arrays

diffly/_conditions.py

@@ -206,11 +206,7 @@ def _compare_sequence_columns(
         n_elements = dtype_right.shape[0]
         has_same_length = col_left.list.len().eq(pl.lit(n_elements))
     else:  # pl.List vs pl.List
-        if not isinstance(max_list_length, int):
-            # Fallback for nested list comparisons where no max_list_length is
-            # available: perform a direct equality comparison without element-wise
-            # unrolling.
-            return _eq_missing(col_left.eq_missing(col_right), col_left, col_right)
+        assert max_list_length is not None
         n_elements = max_list_length
         has_same_length = col_left.list.len().eq_missing(col_right.list.len())
 
@@ -232,7 +228,7 @@ def _get_element(col: pl.Expr, dtype: DataType | DataTypeClass, i: int) -> pl.Ex
                 abs_tol=abs_tol,
                 rel_tol=rel_tol,
                 abs_tol_temporal=abs_tol_temporal,
-                max_list_length=None,
+                max_list_length=max_list_length,
             )
             for i in range(n_elements)
         ]

diffly/comparison.py

@@ -711,22 +711,30 @@ def _validate_subset_of_common_columns(self, subset: Iterable[str]) -> list[str]
 
     @cached_property
     def _max_list_lengths_by_column(self) -> dict[str, int]:
-        list_columns = [
-            col
-            for col in self._other_common_columns
-            if isinstance(self.left_schema[col], pl.List)
-            and isinstance(self.right_schema[col], pl.List)
-        ]
-        if not list_columns:
+        """Max list length across all nesting levels, for columns where both sides
+        contain a List anywhere in their type tree."""
+        left_exprs: list[pl.Expr] = []
+        right_exprs: list[pl.Expr] = []
+        columns: list[str] = []
+
+        for col in self._other_common_columns:
+            col_left = _list_length_exprs(pl.col(col), self.left_schema[col])
+            col_right = _list_length_exprs(pl.col(col), self.right_schema[col])
+            if not (col_left and col_right):
+                continue
+            columns.append(col)
+            left_exprs.append(pl.max_horizontal(col_left).alias(col))
+            right_exprs.append(pl.max_horizontal(col_right).alias(col))
+
+        if not columns:
             return {}
 
-        exprs = [pl.col(col).list.len().max().alias(col) for col in list_columns]
         [left_max, right_max] = pl.collect_all(
-            [self.left.select(exprs), self.right.select(exprs)]
+            [self.left.select(left_exprs), self.right.select(right_exprs)]
         )
         return {
             col: max(int(left_max[col].item() or 0), int(right_max[col].item() or 0))
-            for col in list_columns
+            for col in columns
         }
 
     def _condition_equal_rows(self, columns: list[str]) -> pl.Expr:
@@ -833,3 +841,21 @@ def right_only(self) -> Schema:
         """Columns that are only present in the right data frame, mapped to their data
         types."""
         return self.right() - self.left()
+
+
+def _list_length_exprs(
+    expr: pl.Expr, dtype: pl.DataType | pl.datatypes.DataTypeClass
+) -> list[pl.Expr]:
+    """Collect max-list-length scalar expressions for every List level in the type
+    tree."""
+    if isinstance(dtype, pl.List):
+        return [expr.list.len().max(), *_list_length_exprs(expr.explode(), dtype.inner)]
+    if isinstance(dtype, pl.Array):
+        return _list_length_exprs(expr.explode(), dtype.inner)
+    if isinstance(dtype, pl.Struct):
+        return [
+            e
+            for field in dtype.fields
+            for e in _list_length_exprs(expr.struct[field.name], field.dtype)
+        ]
+    return []

tests/test_conditions.py

@@ -102,6 +102,10 @@ def test_condition_equal_columns_list_array_with_tolerance(
         schema={"pk": pl.Int64, "a_right": rhs_type},
     )
 
+    max_list_length: int | None = None
+    if isinstance(lhs_type, pl.List) and isinstance(rhs_type, pl.List):
+        max_list_length = 2
+
     # Act
     actual = (
         lhs.join(rhs, on="pk", maintain_order="left")
@@ -112,7 +116,7 @@ def test_condition_equal_columns_list_array_with_tolerance(
                 dtype_right=rhs.schema["a_right"],
                 abs_tol=0.5,
                 rel_tol=0,
-                max_list_length=2,
+                max_list_length=max_list_length,
             )
         )
         .to_series()
@@ -156,6 +160,10 @@ def test_condition_equal_columns_nested_list_array_with_tolerance(
         schema={"pk": pl.Int64, "a_right": rhs_type},
     )
 
+    max_list_length: int | None = None
+    if isinstance(lhs_type, pl.List) and isinstance(rhs_type, pl.List):
+        max_list_length = 3
+
     # Act
     actual = (
         lhs.join(rhs, on="pk", maintain_order="left")
@@ -166,16 +174,13 @@ def test_condition_equal_columns_nested_list_array_with_tolerance(
                 dtype_right=rhs.schema["a_right"],
                 abs_tol=0.5,
                 rel_tol=0,
-                max_list_length=2,
+                max_list_length=max_list_length,
             )
         )
         .to_series()
     )
 
-    if isinstance(lhs_type, pl.List) and isinstance(rhs_type, pl.List):
-        assert actual.to_list() == [True, False, False]
-    else:
-        assert actual.to_list() == [True, True, False]
+    assert actual.to_list() == [True, True, False]
 
 
 def test_condition_equal_columns_nested_dtype_mismatch() -> None:
@@ -201,7 +206,7 @@ def test_condition_equal_columns_nested_dtype_mismatch() -> None:
                 "a",
                 dtype_left=lhs.schema["a_left"],
                 dtype_right=rhs.schema["a_right"],
-                max_list_length=None,
+                max_list_length=2,
             )
         )
         .to_series()
@@ -341,7 +346,7 @@ def test_condition_equal_columns_array_vs_list_length_mismatch() -> None:
                 "a",
                 dtype_left=lhs.schema["a_left"],
                 dtype_right=rhs.schema["a_right"],
-                max_list_length=None,
+                max_list_length=2,
                 abs_tol=0.5,
                 rel_tol=0,
             )
@@ -406,21 +411,59 @@ def test_condition_equal_columns_empty_list_array(
         schema={"pk": pl.Int64, "a_right": rhs_type},
     )
 
+    max_list_length: int | None = None
+    if isinstance(lhs_type, pl.List) or isinstance(rhs_type, pl.List):
+        max_list_length = 0
+
     actual = (
         lhs.join(rhs, on="pk", maintain_order="left")
         .select(
             condition_equal_columns(
                 "a",
                 dtype_left=lhs.schema["a_left"],
                 dtype_right=rhs.schema["a_right"],
-                max_list_length=None,
+                max_list_length=max_list_length,
             )
         )
         .to_series()
     )
     assert actual.to_list() == [True, True]
 
 
+def test_condition_equal_columns_lists_only_inner() -> None:
+    # Arrange
+    lhs = pl.DataFrame(
+        {
+            "pk": [1, 2],
+            "a_left": [{"x": 1, "y": [1.0, 2.0, 3.0]}, {"x": 2, "y": [4.0, 5.0, 6.0]}],
+        },
+    )
+    rhs = pl.DataFrame(
+        {
+            "pk": [1, 2],
+            "a_right": [{"x": 1, "y": [1.0, 2.1, 3.0]}, {"x": 2, "y": [4.0, 5.3, 6.0]}],
+        },
+    )
+
+    # Act
+    actual = (
+        lhs.join(rhs, on="pk", maintain_order="left")
+        .select(
+            condition_equal_columns(
+                "a",
+                dtype_left=lhs.schema["a_left"],
+                dtype_right=rhs.schema["a_right"],
+                max_list_length=3,
+                abs_tol=0.2,
+            )
+        )
+        .to_series()
+    )
+
+    # Assert
+    assert actual.to_list() == [True, False]
+
+
 @pytest.mark.parametrize(
     ("dtype_left", "dtype_right", "can_compare_dtypes"),
     [