99 lines
3.3 KiB
Python
99 lines
3.3 KiB
Python
"""
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Cross-encoder neural reranking for search results.
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"""
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from typing import List
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from .types import MergedCandidate, ScoredResult
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class CrossEncoderReranker:
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"""
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Neural reranking using a cross-encoder model.
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Configured via environment variables (see cross_encoder.py).
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Default local model is cross-encoder/ms-marco-MiniLM-L-6-v2.
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"""
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def __init__(self, cross_encoder=None):
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"""
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Initialize cross-encoder reranker.
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Args:
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cross_encoder: CrossEncoderModel instance. If None, creates one from
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environment variables (defaults to local provider)
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"""
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if cross_encoder is None:
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from hindsight_api.engine.cross_encoder import create_cross_encoder_from_env
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cross_encoder = create_cross_encoder_from_env()
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self.cross_encoder = cross_encoder
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def rerank(
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self,
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query: str,
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candidates: List[MergedCandidate]
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) -> List[ScoredResult]:
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"""
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Rerank candidates using cross-encoder scores.
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Args:
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query: Search query
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candidates: Merged candidates from RRF
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Returns:
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List of ScoredResult objects sorted by cross-encoder score
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"""
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if not candidates:
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return []
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# Prepare query-document pairs with date information
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pairs = []
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for candidate in candidates:
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retrieval = candidate.retrieval
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# Use text + context for better ranking
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doc_text = retrieval.text
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if retrieval.context:
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doc_text = f"{retrieval.context}: {doc_text}"
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# Add formatted date information for temporal awareness
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if retrieval.occurred_start:
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occurred_start = retrieval.occurred_start
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# Format in two styles for better model understanding
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# 1. ISO format: YYYY-MM-DD
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date_iso = occurred_start.strftime("%Y-%m-%d")
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# 2. Human-readable: "June 5, 2022"
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date_readable = occurred_start.strftime("%B %d, %Y")
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# Prepend date to document text
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doc_text = f"[Date: {date_readable} ({date_iso})] {doc_text}"
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pairs.append([query, doc_text])
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# Get cross-encoder scores
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scores = self.cross_encoder.predict(pairs)
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# Normalize scores using sigmoid to [0, 1] range
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# Cross-encoder returns logits which can be negative
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import numpy as np
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def sigmoid(x):
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return 1 / (1 + np.exp(-x))
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normalized_scores = [sigmoid(score) for score in scores]
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# Create ScoredResult objects with cross-encoder scores
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scored_results = []
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for candidate, raw_score, norm_score in zip(candidates, scores, normalized_scores):
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scored_result = ScoredResult(
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candidate=candidate,
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cross_encoder_score=float(raw_score),
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cross_encoder_score_normalized=float(norm_score),
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weight=float(norm_score) # Initial weight is just cross-encoder score
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)
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scored_results.append(scored_result)
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# Sort by cross-encoder score
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scored_results.sort(key=lambda x: x.weight, reverse=True)
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return scored_results
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