Add Dist Metrics for String Distance Evaluation (#8837)

Co-authored-by: shibuiwilliam <shibuiyusuke@gmail.com>

libs/langchain/langchain/evaluation/string_distance/base.py

@@ -43,12 +43,16 @@ class StringDistance(str, Enum):
         LEVENSHTEIN: The Levenshtein distance.
         JARO: The Jaro distance.
         JARO_WINKLER: The Jaro-Winkler distance.
+        HAMMING: The Hamming distance.
+        INDEL: The Indel distance.
     """
 
     DAMERAU_LEVENSHTEIN = "damerau_levenshtein"
     LEVENSHTEIN = "levenshtein"
     JARO = "jaro"
     JARO_WINKLER = "jaro_winkler"
+    HAMMING = "hamming"
+    INDEL = "indel"
 
 
 class _RapidFuzzChainMixin(Chain):
@@ -99,7 +103,7 @@ class _RapidFuzzChainMixin(Chain):
         return result
 
     @staticmethod
-    def _get_metric(distance: str) -> Callable:
+    def _get_metric(distance: str, normalize_score: bool = False) -> Callable:
         """
         Get the distance metric function based on the distance type.
 
@@ -112,17 +116,26 @@ class _RapidFuzzChainMixin(Chain):
         Raises:
             ValueError: If the distance metric is invalid.
         """
-        rf_distance = _load_rapidfuzz()
-        if distance == StringDistance.DAMERAU_LEVENSHTEIN:
-            return rf_distance.DamerauLevenshtein.distance
-        elif distance == StringDistance.LEVENSHTEIN:
-            return rf_distance.Levenshtein.distance
-        elif distance == StringDistance.JARO:
-            return rf_distance.Jaro.distance
-        elif distance == StringDistance.JARO_WINKLER:
-            return rf_distance.JaroWinkler.distance
+        from rapidfuzz import distance as rf_distance
+
+        module_map: Dict[str, Any] = {
+            StringDistance.DAMERAU_LEVENSHTEIN: rf_distance.DamerauLevenshtein,
+            StringDistance.LEVENSHTEIN: rf_distance.Levenshtein,
+            StringDistance.JARO: rf_distance.Jaro,
+            StringDistance.JARO_WINKLER: rf_distance.JaroWinkler,
+            StringDistance.HAMMING: rf_distance.Hamming,
+            StringDistance.INDEL: rf_distance.Indel,
+        }
+        if distance not in module_map:
+            raise ValueError(
+                f"Invalid distance metric: {distance}"
+                f"\nMust be one of: {list(StringDistance)}"
+            )
+        module = module_map[distance]
+        if normalize_score:
+            return module.normalized_distance
         else:
-            raise ValueError(f"Invalid distance metric: {distance}")
+            return module.distance
 
     @property
     def metric(self) -> Callable:
@@ -132,7 +145,9 @@ class _RapidFuzzChainMixin(Chain):
         Returns:
             Callable: The distance metric function.
         """
-        return _RapidFuzzChainMixin._get_metric(self.distance)
+        return _RapidFuzzChainMixin._get_metric(
+            self.distance, normalize_score=self.normalize_score
+        )
 
     def compute_metric(self, a: str, b: str) -> float:
         """
@@ -145,13 +160,7 @@ class _RapidFuzzChainMixin(Chain):
         Returns:
             float: The distance between the two strings.
         """
-        score = self.metric(a, b)
-        if self.normalize_score and self.distance in (
-            StringDistance.DAMERAU_LEVENSHTEIN,
-            StringDistance.LEVENSHTEIN,
-        ):
-            score = score / max(len(a), len(b))
-        return score
+        return self.metric(a, b)
 
 
 class StringDistanceEvalChain(StringEvaluator, _RapidFuzzChainMixin):

libs/langchain/tests/unit_tests/evaluation/string_distance/test_base.py

@@ -30,8 +30,13 @@ async def test_zero_distance_async(distance: StringDistance) -> None:
 
 @pytest.mark.requires("rapidfuzz")
 @pytest.mark.parametrize("distance", list(StringDistance))
-def test_zero_distance_pairwise(distance: StringDistance) -> None:
-    eval_chain = PairwiseStringDistanceEvalChain(distance=distance)
+@pytest.mark.parametrize("normalize_score", [True, False])
+def test_zero_distance_pairwise(
+    distance: StringDistance, normalize_score: bool
+) -> None:
+    eval_chain = PairwiseStringDistanceEvalChain(
+        distance=distance, normalize_score=normalize_score
+    )
     string = "三人行则必有我师"
     result = eval_chain.evaluate_string_pairs(prediction=string, prediction_b=string)
     assert "score" in result
@@ -49,3 +54,60 @@ async def test_zero_distance_pairwise_async(distance: StringDistance) -> None:
     )
     assert "score" in result
     assert result["score"] == 0
+
+
+@pytest.mark.requires("rapidfuzz")
+@pytest.mark.parametrize("distance", list(StringDistance))
+@pytest.mark.parametrize("normalize_score", [True, False])
+def test_non_zero_distance(distance: StringDistance, normalize_score: bool) -> None:
+    eval_chain = StringDistanceEvalChain(
+        distance=distance, normalize_score=normalize_score
+    )
+    prediction = "I like to eat apples."
+    reference = "I like apples."
+    result = eval_chain.evaluate_strings(prediction=prediction, reference=reference)
+    assert "score" in result
+    assert 0 < result["score"]
+    if normalize_score:
+        assert result["score"] < 1.0
+
+
+@pytest.mark.asyncio
+@pytest.mark.requires("rapidfuzz")
+@pytest.mark.parametrize("distance", list(StringDistance))
+async def test_non_zero_distance_async(distance: StringDistance) -> None:
+    eval_chain = StringDistanceEvalChain(distance=distance)
+    prediction = "I like to eat apples."
+    reference = "I like apples."
+    result = await eval_chain.aevaluate_strings(
+        prediction=prediction, reference=reference
+    )
+    assert "score" in result
+    assert 0 < result["score"] < 1.0
+
+
+@pytest.mark.requires("rapidfuzz")
+@pytest.mark.parametrize("distance", list(StringDistance))
+def test_non_zero_distance_pairwise(distance: StringDistance) -> None:
+    eval_chain = PairwiseStringDistanceEvalChain(distance=distance)
+    prediction = "I like to eat apples."
+    reference = "I like apples."
+    result = eval_chain.evaluate_string_pairs(
+        prediction=prediction, prediction_b=reference
+    )
+    assert "score" in result
+    assert 0 < result["score"] < 1.0
+
+
+@pytest.mark.asyncio
+@pytest.mark.requires("rapidfuzz")
+@pytest.mark.parametrize("distance", list(StringDistance))
+async def test_non_zero_distance_pairwise_async(distance: StringDistance) -> None:
+    eval_chain = PairwiseStringDistanceEvalChain(distance=distance)
+    prediction = "I like to eat apples."
+    reference = "I like apples."
+    result = await eval_chain.aevaluate_string_pairs(
+        prediction=prediction, prediction_b=reference
+    )
+    assert "score" in result
+    assert 0 < result["score"] < 1.0

libs/langchain/tests/unit_tests/evaluation/test_loading.py

@@ -1,4 +1,5 @@
 """Test the loading function for evaluators."""
+from typing import List
 
 import pytest
 
@@ -26,24 +27,31 @@ def test_load_evaluators(evaluator_type: EvaluatorType) -> None:
 
 
 @pytest.mark.parametrize(
-    "evaluator_type",
+    "evaluator_types",
     [
-        EvaluatorType.LABELED_CRITERIA,
-        EvaluatorType.LABELED_PAIRWISE_STRING,
-        EvaluatorType.QA,
-        EvaluatorType.CONTEXT_QA,
-        EvaluatorType.COT_QA,
+        [EvaluatorType.LABELED_CRITERIA],
+        [EvaluatorType.LABELED_PAIRWISE_STRING],
+        [EvaluatorType.QA],
+        [EvaluatorType.CONTEXT_QA],
+        [EvaluatorType.COT_QA],
+        [EvaluatorType.COT_QA, EvaluatorType.LABELED_CRITERIA],
+        [
+            EvaluatorType.COT_QA,
+            EvaluatorType.LABELED_CRITERIA,
+            EvaluatorType.LABELED_PAIRWISE_STRING,
+        ],
     ],
 )
-def test_eval_chain_requires_references(evaluator_type: EvaluatorType) -> None:
+def test_eval_chain_requires_references(evaluator_types: List[EvaluatorType]) -> None:
     """Test loading evaluators."""
     fake_llm = FakeLLM(
         queries={"text": "The meaning of life\nCORRECT"}, sequential_responses=True
     )
-    evaluator = load_evaluators(
-        [evaluator_type],
+    evaluators = load_evaluators(
+        evaluator_types,
         llm=fake_llm,
-    )[0]
-    if not isinstance(evaluator, (StringEvaluator, PairwiseStringEvaluator)):
-        raise ValueError("Evaluator is not a [pairwise]string evaluator")
-    assert evaluator.requires_reference
+    )
+    for evaluator in evaluators:
+        if not isinstance(evaluator, (StringEvaluator, PairwiseStringEvaluator)):
+            raise ValueError("Evaluator is not a [pairwise]string evaluator")
+        assert evaluator.requires_reference