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113 lines
3.6 KiB
Python
113 lines
3.6 KiB
Python
"""Select and order examples based on ngram overlap score (sentence_bleu score).
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https://www.nltk.org/_modules/nltk/translate/bleu_score.html
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https://aclanthology.org/P02-1040.pdf
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"""
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from typing import Dict, List
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import numpy as np
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from pydantic import BaseModel, root_validator
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from langchain.prompts.example_selector.base import BaseExampleSelector
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from langchain.prompts.prompt import PromptTemplate
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def ngram_overlap_score(source: List[str], example: List[str]) -> float:
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"""Compute ngram overlap score of source and example as sentence_bleu score.
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Use sentence_bleu with method1 smoothing function and auto reweighting.
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Return float value between 0.0 and 1.0 inclusive.
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https://www.nltk.org/_modules/nltk/translate/bleu_score.html
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https://aclanthology.org/P02-1040.pdf
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"""
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from nltk.translate.bleu_score import (
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SmoothingFunction, # type: ignore
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sentence_bleu,
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)
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hypotheses = source[0].split()
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references = [s.split() for s in example]
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return float(
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sentence_bleu(
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references,
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hypotheses,
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smoothing_function=SmoothingFunction().method1,
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auto_reweigh=True,
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)
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)
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class NGramOverlapExampleSelector(BaseExampleSelector, BaseModel):
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"""Select and order examples based on ngram overlap score (sentence_bleu score).
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https://www.nltk.org/_modules/nltk/translate/bleu_score.html
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https://aclanthology.org/P02-1040.pdf
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"""
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examples: List[dict]
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"""A list of the examples that the prompt template expects."""
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example_prompt: PromptTemplate
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"""Prompt template used to format the examples."""
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threshold: float = -1.0
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"""Threshold at which algorithm stops. Set to -1.0 by default.
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For negative threshold:
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select_examples sorts examples by ngram_overlap_score, but excludes none.
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For threshold greater than 1.0:
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select_examples excludes all examples, and returns an empty list.
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For threshold equal to 0.0:
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select_examples sorts examples by ngram_overlap_score,
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and excludes examples with no ngram overlap with input.
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"""
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@root_validator(pre=True)
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def check_dependencies(cls, values: Dict) -> Dict:
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"""Check that valid dependencies exist."""
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try:
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from nltk.translate.bleu_score import ( # noqa: disable=F401
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SmoothingFunction,
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sentence_bleu,
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)
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except ImportError as e:
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raise ValueError(
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"Not all the correct dependencies for this ExampleSelect exist"
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) from e
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return values
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def add_example(self, example: Dict[str, str]) -> None:
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"""Add new example to list."""
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self.examples.append(example)
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def select_examples(self, input_variables: Dict[str, str]) -> List[dict]:
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"""Return list of examples sorted by ngram_overlap_score with input.
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Descending order.
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Excludes any examples with ngram_overlap_score less than or equal to threshold.
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"""
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inputs = list(input_variables.values())
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examples = []
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k = len(self.examples)
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score = [0.0] * k
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first_prompt_template_key = self.example_prompt.input_variables[0]
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for i in range(k):
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score[i] = ngram_overlap_score(
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inputs, [self.examples[i][first_prompt_template_key]]
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)
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while True:
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arg_max = np.argmax(score)
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if (score[arg_max] < self.threshold) or abs(
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score[arg_max] - self.threshold
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) < 1e-9:
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break
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examples.append(self.examples[arg_max])
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score[arg_max] = self.threshold - 1.0
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return examples
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