ArraySubset defined, first draft

splink/comparison_level_library.py

@@ -3,6 +3,7 @@
     AbsoluteTimeDifferenceLevel,
     And,
     ArrayIntersectLevel,
+    ArraySubsetLevel,
     ColumnsReversedLevel,
     CustomLevel,
     DamerauLevenshteinLevel,
@@ -38,6 +39,7 @@
     "AbsoluteDateDifferenceLevel",
     "DistanceInKMLevel",
     "ArrayIntersectLevel",
+    "ArraySubsetLevel",
     "PercentageDifferenceLevel",
     "And",
     "Not",

splink/internals/comparison_level_library.py

@@ -806,6 +806,40 @@ def create_label_for_charts(self) -> str:
         return f"Array intersection size >= {self.min_intersection}"
 
 
+class ArraySubsetLevel(ComparisonLevelCreator):
+    def __init__(self, col_name: str | ColumnExpression):
+        """Represents a comparison level where the smaller array is an
+        exact subset of the larger array.
+        """
+        self.col_expression = ColumnExpression.instantiate_if_str(col_name)
+
+    @unsupported_splink_dialects(["sqlite"])
+    def create_sql(self, sql_dialect: SplinkDialect) -> str:
+        sqlglot_dialect_name = sql_dialect.sqlglot_name
+
+        sqlglot_base_dialect_sql = """
+            LEAST(ARRAY_SIZE(___col____l), ARRAY_SIZE(___col____r))<>0
+            AND
+            ARRAY_SIZE(
+            ARRAY_INTERSECT(___col____l, ___col____r)) /
+            LEAST(ARRAY_SIZE(___col____l), ARRAY_SIZE(___col____r))
+            == 1
+            """
+        translated = _translate_sql_string(
+            sqlglot_base_dialect_sql, sqlglot_dialect_name
+        )
+
+        self.col_expression.sql_dialect = sql_dialect
+        col = self.col_expression
+        col = self.col_expression
+        translated = translated.replace("___col____l", col.name_l)
+        translated = translated.replace("___col____r", col.name_r)
+        return translated
+
+    def create_label_for_charts(self) -> str:
+        return "Array subset"
+
+
 class PercentageDifferenceLevel(ComparisonLevelCreator):
     def __init__(self, col_name: str, percentage_threshold: float):
         """

tests/test_array_columns.py

@@ -1,8 +1,10 @@
 import pytest
 
+import splink.internals.comparison_level_library as cll
 import splink.internals.comparison_library as cl
 from tests.decorator import mark_with_dialects_excluding
 from tests.literal_utils import (
+    ComparisonLevelTestSpec,
     ComparisonTestSpec,
     LiteralTestValues,
     run_tests_with_args,
@@ -72,3 +74,37 @@ def test_array_comparison_1(test_helpers, dialect):
         cl.ArrayIntersectAtSizes("postcode", [-1, 2]).get_comparison(
             db_api.sql_dialect.sqlglot_name
         )
+
+
+# No SQLite - no array comparisons in library
+@mark_with_dialects_excluding("sqlite")
+def test_array_subset(test_helpers, dialect):
+    helper = test_helpers[dialect]
+    db_api = helper.extra_linker_args()["db_api"]
+
+    test_spec = ComparisonLevelTestSpec(
+        cll.ArraySubsetLevel("arr"),
+        tests=[
+            LiteralTestValues(
+                {"arr_l": ["A", "B", "C", "D"], "arr_r": ["A", "B", "C", "D"]},
+                expected_in_level=True,
+            ),
+            LiteralTestValues(
+                {"arr_l": ["A", "B", "C", "D"], "arr_r": ["A", "B", "C", "Z"]},
+                expected_in_level=False,
+            ),
+            LiteralTestValues(
+                {"arr_l": ["A", "B"], "arr_r": ["A", "B", "C", "D"]},
+                expected_in_level=True,
+            ),
+            LiteralTestValues(
+                {"arr_l": ["A", "B", "C", "D"], "arr_r": ["X", "Y", "Z"]},
+                expected_in_level=False,
+            ),
+            LiteralTestValues(
+                {"arr_l": [], "arr_r": ["X", "Y", "Z"]},
+                expected_in_level=False,
+            ),
+        ],
+    )
+    run_tests_with_args(test_spec, db_api)