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"""Annif backend using a SVM classifier""" |
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from __future__ import annotations |
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import os.path |
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from typing import TYPE_CHECKING, Any |
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import joblib |
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import numpy as np |
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import scipy.special |
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from sklearn.svm import LinearSVC |
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import annif.util |
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from annif.exception import NotInitializedException, NotSupportedException |
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from annif.suggestion import SubjectSuggestion, SuggestionBatch |
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from . import backend, mixins |
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if TYPE_CHECKING: |
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from scipy.sparse._csr import csr_matrix |
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from annif.corpus.document import DocumentCorpus |
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class SVCBackend(mixins.TfidfVectorizerMixin, backend.AnnifBackend): |
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"""Support vector classifier backend for Annif""" |
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name = "svc" |
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# defaults for uninitialized instances |
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_model = None |
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MODEL_FILE = "svc-model.gz" |
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DEFAULT_PARAMETERS = {"min_df": 1, "ngram": 1} |
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def _initialize_model(self) -> None: |
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if self._model is None: |
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path = os.path.join(self.datadir, self.MODEL_FILE) |
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self.debug("loading model from {}".format(path)) |
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if os.path.exists(path): |
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self._model = joblib.load(path) |
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else: |
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raise NotInitializedException( |
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"model {} not found".format(path), backend_id=self.backend_id |
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) |
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def initialize(self, parallel: bool = False) -> None: |
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self.initialize_vectorizer() |
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self._initialize_model() |
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def _corpus_to_texts_and_classes( |
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self, corpus: DocumentCorpus |
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) -> tuple[list[str], list[int]]: |
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texts = [] |
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classes = [] |
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for doc in corpus.documents: |
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if len(doc.subject_set) > 1: |
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self.warning( |
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"training on a document with multiple subjects is not " |
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+ "supported by SVC; selecting one random subject." |
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) |
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elif not doc.subject_set: |
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continue # skip documents with no subjects |
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texts.append(doc.text) |
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classes.append(doc.subject_set[0]) |
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return texts, classes |
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def _train_classifier(self, veccorpus: csr_matrix, classes: list[int]) -> None: |
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self.info("creating classifier") |
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self._model = LinearSVC() |
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self._model.fit(veccorpus, classes) |
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annif.util.atomic_save( |
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self._model, self.datadir, self.MODEL_FILE, method=joblib.dump |
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) |
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def _train( |
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self, corpus: DocumentCorpus, params: dict[str, Any], jobs: int = 0 |
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) -> None: |
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if corpus == "cached": |
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raise NotSupportedException( |
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"SVC backend does not support reuse of cached training data." |
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) |
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if corpus.is_empty(): |
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raise NotSupportedException("Cannot train SVC project with no documents") |
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texts, classes = self._corpus_to_texts_and_classes(corpus) |
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vecparams = { |
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"min_df": int(params["min_df"]), |
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"tokenizer": self.project.analyzer.tokenize_words, |
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"ngram_range": (1, int(params["ngram"])), |
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} |
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veccorpus = self.create_vectorizer(texts, vecparams) |
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self._train_classifier(veccorpus, classes) |
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def _scores_to_suggestions( |
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self, scores: np.ndarray, params: dict[str, Any] |
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) -> list[SubjectSuggestion]: |
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results = [] |
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limit = int(params["limit"]) |
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for class_id in np.argsort(scores)[::-1][:limit]: |
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subject_id = self._model.classes_[class_id] |
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if subject_id is not None: |
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results.append( |
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SubjectSuggestion(subject_id=subject_id, score=scores[class_id]) |
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) |
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return results |
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def _suggest_batch( |
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self, texts: list[str], params: dict[str, Any] |
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) -> SuggestionBatch: |
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vector = self.vectorizer.transform(texts) |
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confidences = self._model.decision_function(vector) |
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# convert to 0..1 score range using logistic function |
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scores_list = scipy.special.expit(confidences) |
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return SuggestionBatch.from_sequence( |
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[ |
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[] if row.nnz == 0 else self._scores_to_suggestions(scores, params) |
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for scores, row in zip(scores_list, vector) |
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], |
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self.project.subjects, |
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) |
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NatLibFi /
Annif
