Add Levenshtein distance (#191)

* Add Levenshtein distance

* Fix linting and formatting

* Fix matrix plot ranges

Author: ruivieira

src/trustyai/metrics/distance.py

@@ -0,0 +1,117 @@
+""""Distance metrics"""
+# pylint: disable = import-error
+from dataclasses import dataclass
+from typing import List, Optional, Union, Callable
+
+from org.kie.trustyai.metrics.language.distance import (
+    Levenshtein as _Levenshtein,
+    LevenshteinResult as _LevenshteinResult,
+    LevenshteinCounters as _LevenshteinCounters,
+)
+from opennlp.tools.tokenize import Tokenizer
+import numpy as np
+import matplotlib.pyplot as plt
+from trustyai import _default_initializer  # pylint: disable=unused-import
+
+
+@dataclass
+class LevenshteinCounters:
+    """LevenshteinCounters Counters"""
+
+    substitutions: int
+    insertions: int
+    deletions: int
+    correct: int
+
+    @staticmethod
+    def convert(result: _LevenshteinCounters):
+        """Converts a Java LevenshteinCounters to a Python LevenshteinCounters"""
+        return LevenshteinCounters(
+            substitutions=result.getSubstitutions(),
+            insertions=result.getInsertions(),
+            deletions=result.getDeletions(),
+            correct=result.getCorrect(),
+        )
+
+
+@dataclass
+class LevenshteinResult:
+    """Levenshtein Result"""
+
+    distance: float
+    counters: LevenshteinCounters
+    matrix: np.ndarray
+    reference: List[str]
+    hypothesis: List[str]
+
+    @staticmethod
+    def convert(result: _LevenshteinResult):
+        """Converts a Java LevenshteinResult to a Python LevenshteinResult"""
+        distance = result.getDistance()
+        counters = LevenshteinCounters.convert(result.getCounters())
+        data = result.getDistanceMatrix().getData()
+        numpy_array = np.array(data)[1:, 1:]
+        reference = result.getReferenceTokens()
+        hypothesis = result.getHypothesisTokens()
+
+        return LevenshteinResult(
+            distance=distance,
+            counters=counters,
+            matrix=numpy_array,
+            reference=reference,
+            hypothesis=hypothesis,
+        )
+
+    def plot(self):
+        """Plot the Levenshtein distance matrix"""
+        cmap = plt.cm.viridis
+
+        _, axes = plt.subplots()
+        cax = axes.imshow(self.matrix, cmap=cmap, interpolation="nearest")
+
+        plt.colorbar(cax)
+
+        axes.set_xticks(np.arange(len(self.reference)))
+        axes.set_yticks(np.arange(len(self.hypothesis)))
+        axes.set_xticklabels(self.reference)
+        axes.set_yticklabels(self.hypothesis)
+
+        plt.setp(
+            axes.get_xticklabels(), rotation=45, ha="right", rotation_mode="anchor"
+        )
+
+        nrows, ncols = self.matrix.shape
+        for i in range(nrows):
+            for j in range(ncols):
+                color = (
+                    "white" if self.matrix[i, j] < self.matrix.max() / 2 else "black"
+                )
+                axes.text(
+                    j, i, int(self.matrix[i, j]), ha="center", va="center", color=color
+                )
+
+        plt.show()
+
+
+def levenshtein(
+    reference: str,
+    hypothesis: str,
+    tokenizer: Optional[Union[Tokenizer, Callable[[str], List[str]]]] = None,
+) -> LevenshteinResult:
+    """Calculate Levenshtein distance between two strings"""
+    if not tokenizer:
+        return LevenshteinResult.convert(
+            _Levenshtein.calculateToken(reference, hypothesis)
+        )
+    if isinstance(tokenizer, Tokenizer):
+        return LevenshteinResult.convert(
+            _Levenshtein.calculateToken(reference, hypothesis, tokenizer)
+        )
+    if callable(tokenizer):
+        tokenized_reference = tokenizer(reference)
+        tokenized_hypothesis = tokenizer(hypothesis)
+        return LevenshteinResult.convert(
+            _Levenshtein.calculateToken(tokenized_reference, tokenized_hypothesis)
+        )
+
+    raise ValueError("Unsupported tokenizer")

src/trustyai/metrics/language.py

@@ -1,24 +1,17 @@
-""""Group fairness metrics"""
+""""Language metrics"""
+# pylint: disable = import-error
 from dataclasses import dataclass
 
-# pylint: disable = import-error
 from typing import List, Optional, Union, Callable
 
 from org.kie.trustyai.metrics.language.levenshtein import (
     WordErrorRate as _WordErrorRate,
     ErrorRateResult as _ErrorRateResult,
 )
 from opennlp.tools.tokenize import Tokenizer
+from trustyai import _default_initializer  # pylint: disable=unused-import
 
-
-@dataclass
-class LevenshteinCounters:
-    """LevenshteinCounters Counters"""
-
-    substitutions: int
-    insertions: int
-    deletions: int
-    correct: int
+from .distance import LevenshteinCounters
 
 
 @dataclass