feat: refactor training

model2vec/inference/model.py

@@ -2,6 +2,7 @@
 
 import re
 from collections.abc import Sequence
+from enum import Enum
 from pathlib import Path
 from tempfile import TemporaryDirectory
 from typing import TypeVar, cast
@@ -23,25 +24,26 @@
 LabelType = TypeVar("LabelType", list[str], list[list[str]])
 
 
+class HeadType(str, Enum):
+    CLASSIFIER = "classifier"
+    PROJECTOR = "projector"
+    MULTILABEL = "multilabel"
+
+
 class StaticModelPipeline:
     def __init__(self, model: StaticModel, head: Pipeline) -> None:
         """Create a pipeline with a StaticModel encoder."""
         self.model = model
         self.head = head
-        classifier = self.head[-1]
-        # Check if the classifier is a multilabel classifier.
-        # NOTE: this doesn't look robust, but it is.
-        # Different classifiers, such as OVR wrappers, support multilabel output natively, so we
-        # can just use predict.
-        self.multilabel = False
-        if isinstance(classifier, MLPClassifier):
-            if classifier.out_activation_ == "logistic":
-                self.multilabel = True
-
-    @property
-    def classes_(self) -> np.ndarray:
-        """The classes of the classifier."""
-        return self.head.classes_
+
+        last_head = self.head[-1]
+        self.classes_: None | np.ndarray = None
+        if isinstance(last_head, MLPClassifier):
+            activation = last_head.out_activation_
+            self.classifier_type = HeadType.MULTILABEL if activation == "logistic" else HeadType.CLASSIFIER
+            self.classes_ = self.head.classes_
+        else:
+            self.classifier_type = HeadType.PROJECTOR
 
     @classmethod
     def from_pretrained(
@@ -138,7 +140,8 @@ def predict(
             multiprocessing_threshold=multiprocessing_threshold,
         )
 
-        if self.multilabel:
+        if self.classifier_type == HeadType.MULTILABEL:
+            assert self.classes_ is not None
             out_labels = []
             proba = self.head.predict_proba(encoded)
             for vector in proba:
@@ -166,7 +169,10 @@ def predict_proba(
         :param use_multiprocessing: Whether to use multiprocessing for encoding. Defaults to True.
         :param multiprocessing_threshold: The threshold for the number of samples to use multiprocessing. Defaults to 10,000.
         :return: The predicted labels or probabilities.
+        :raises ValueError: If the classifier type is projector.
         """
+        if self.classifier_type == HeadType.PROJECTOR:
+            raise ValueError("You are using evaluate on a projector model. This is not supported.")
         encoded = self._encode_and_coerce_to_2d(
             X,
             show_progress_bar=show_progress_bar,
@@ -190,7 +196,10 @@ def evaluate(
         :param threshold: The threshold for multilabel classification.
         :param output_dict: Whether to output the classification report as a dictionary.
         :return: A classification report.
+        :raises ValueError: If the classifier type is projector.
         """
+        if self.classifier_type == HeadType.PROJECTOR:
+            raise ValueError("You are using evaluate on a projector model. This is not supported.")
         predictions = self.predict(X, show_progress_bar=True, batch_size=batch_size, threshold=threshold)
         report = evaluate_single_or_multi_label(predictions=predictions, y=y, output_dict=output_dict)
 

model2vec/train/__init__.py

@@ -6,5 +6,6 @@
     importable(extra_dependency, _REQUIRED_EXTRA)
 
 from model2vec.train.classifier import StaticModelForClassification
+from model2vec.train.similarity import StaticModelForSimilarity
 
-__all__ = ["StaticModelForClassification"]
+__all__ = ["StaticModelForClassification", "StaticModelForSimilarity"]