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"""Hypothetical Document Embeddings.
https://arxiv.org/abs/2212.10496
"""
from __future__ import annotations
from typing import Dict, List
import numpy as np
from pydantic import BaseModel, Extra
from langchain.chains.base import Chain
from langchain.chains.hyde.prompts import PROMPT_MAP
from langchain.chains.llm import LLMChain
from langchain.embeddings.base import Embeddings
from langchain.llms.base import BaseLLM
class HypotheticalDocumentEmbedder(Chain, Embeddings, BaseModel):
"""Generate hypothetical document for query, and then embed that.
Based on https://arxiv.org/abs/2212.10496
"""
base_embeddings: Embeddings
llm_chain: LLMChain
class Config:
"""Configuration for this pydantic object."""
extra = Extra.forbid
arbitrary_types_allowed = True
@property
def input_keys(self) -> List[str]:
"""Input keys for Hyde's LLM chain."""
return self.llm_chain.input_keys
@property
def output_keys(self) -> List[str]:
"""Output keys for Hyde's LLM chain."""
return self.llm_chain.output_keys
def embed_documents(self, texts: List[str]) -> List[List[float]]:
"""Call the base embeddings."""
return self.base_embeddings.embed_documents(texts)
def combine_embeddings(self, embeddings: List[List[float]]) -> List[float]:
"""Combine embeddings into final embeddings."""
return list(np.array(embeddings).mean(axis=0))
def embed_query(self, text: str) -> List[float]:
"""Generate a hypothetical document and embedded it."""
var_name = self.llm_chain.input_keys[0]
result = self.llm_chain.generate([{var_name: text}])
documents = [generation.text for generation in result.generations[0]]
embeddings = self.embed_documents(documents)
return self.combine_embeddings(embeddings)
def _call(self, inputs: Dict[str, str]) -> Dict[str, str]:
"""Call the internal llm chain."""
return self.llm_chain._call(inputs)
@classmethod
def from_llm(
cls, llm: BaseLLM, base_embeddings: Embeddings, prompt_key: str
) -> HypotheticalDocumentEmbedder:
"""Load and use LLMChain for a specific prompt key."""
prompt = PROMPT_MAP[prompt_key]
llm_chain = LLMChain(llm=llm, prompt=prompt)
return cls(base_embeddings=base_embeddings, llm_chain=llm_chain)
@property
def _chain_type(self) -> str:
return "hyde_chain"
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