Skip to main content

上下文压缩

检索的一个挑战是，当你将数据导入系统时，通常不知道具体的查询。这意味着与查询相关的最重要的信息可能埋藏在大量无关文本的文档中。将完整的文档通过应用程序传递可能导致更昂贵的LLM调用和更差的响应。

上下文压缩旨在解决这个问题。想法很简单：不要立即按原样返回检索到的文档，而是可以使用给定查询的上下文对其进行压缩，以便仅返回相关信息。这里的“压缩”既指对单个文档内容进行压缩，也指整体上滤除文档。

要使用上下文压缩检索器，您需要：

  • 一个基本的检索器
  • 一个文档压缩器

上下文压缩检索器将查询传递给基本的检索器，获取初始文档并将其通过文档压缩器进行处理。文档压缩器接收一个文档列表，并通过减少文档内容或完全删除文档来缩短列表。

入门指南​

Helper function for printing docs

def pretty_print_docs(docs):
    print(f"\n{'-' * 100}\n".join([f"Document {i+1}:\n\n" + d.page_content for i, d in enumerate(docs)]))

使用纯向量存储检索器​

让我们从初始化一个简单的向量存储检索器并存储 2023 年国情咨文演讲（以分块方式）开始。我们可以看到，给定一个示例问题，我们的检索器返回一个或两个相关文档和几个不相关的文档。而且即使相关的文档中也有很多不相关的信息。

from langchain.text_splitter import CharacterTextSplitter
from langchain.embeddings import OpenAIEmbeddings
from langchain.document_loaders import TextLoader
from langchain.vectorstores import FAISS

documents = TextLoader('../../../state_of_the_union.txt').load()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
texts = text_splitter.split_documents(documents)
retriever = FAISS.from_documents(texts, OpenAIEmbeddings()).as_retriever()

docs = retriever.get_relevant_documents("What did the president say about Ketanji Brown Jackson")
pretty_print_docs(docs)
    Document 1:
    
    Tonight. I call on the Senate to: Pass the Freedom to Vote Act. Pass the John Lewis Voting Rights Act. And while you’re at it, pass the Disclose Act so Americans can know who is funding our elections. 
    
    Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service. 
    
    One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court. 
    
    And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson. One of our nation’s top legal minds, who will continue Justice Breyer’s legacy of excellence.
    ----------------------------------------------------------------------------------------------------
    Document 2:
    
    A former top litigator in private practice. A former federal public defender. And from a family of public school educators and police officers. A consensus builder. Since she’s been nominated, she’s received a broad range of support—from the Fraternal Order of Police to former judges appointed by Democrats and Republicans. 
    
    And if we are to advance liberty and justice, we need to secure the Border and fix the immigration system. 
    
    We can do both. At our border, we’ve installed new technology like cutting-edge scanners to better detect drug smuggling.  
    
    We’ve set up joint patrols with Mexico and Guatemala to catch more human traffickers.  
    
    We’re putting in place dedicated immigration judges so families fleeing persecution and violence can have their cases heard faster. 
    
    We’re securing commitments and supporting partners in South and Central America to host more refugees and secure their own borders.
    ----------------------------------------------------------------------------------------------------
    Document 3:
    
    And for our LGBTQ+ Americans, let’s finally get the bipartisan Equality Act to my desk. The onslaught of state laws targeting transgender Americans and their families is wrong. 
    
    As I said last year, especially to our younger transgender Americans, I will always have your back as your President, so you can be yourself and reach your God-given potential. 
    
    While it often appears that we never agree, that isn’t true. I signed 80 bipartisan bills into law last year. From preventing government shutdowns to protecting Asian-Americans from still-too-common hate crimes to reforming military justice. 
    
    And soon, we’ll strengthen the Violence Against Women Act that I first wrote three decades ago. It is important for us to show the nation that we can come together and do big things. 
    
    So tonight I’m offering a Unity Agenda for the Nation. Four big things we can do together.  
    
    First, beat the opioid epidemic.
    ----------------------------------------------------------------------------------------------------
    Document 4:
    
    Tonight, I’m announcing a crackdown on these companies overcharging American businesses and consumers. 
    
    And as Wall Street firms take over more nursing homes, quality in those homes has gone down and costs have gone up.  
    
    That ends on my watch. 
    
    Medicare is going to set higher standards for nursing homes and make sure your loved ones get the care they deserve and expect. 
    
    We’ll also cut costs and keep the economy going strong by giving workers a fair shot, provide more training and apprenticeships, hire them based on their skills not degrees. 
    
    Let’s pass the Paycheck Fairness Act and paid leave.  
    
    Raise the minimum wage to $15 an hour and extend the Child Tax Credit, so no one has to raise a family in poverty. 
    
    Let’s increase Pell Grants and increase our historic support of HBCUs, and invest in what Jill—our First Lady who teaches full-time—calls America’s best-kept secret: community colleges.

添加上下文压缩使用 LLMChainExtractor​

现在让我们用 ContextualCompressionRetriever 包装我们的基本检索器。我们将添加一个 LLMChainExtractor，它将迭代最初返回的文档，并从每个文档中提取与查询相关的内容。

from langchain.llms import OpenAI
from langchain.retrievers import ContextualCompressionRetriever
from langchain.retrievers.document_compressors import LLMChainExtractor

llm = OpenAI(temperature=0)
compressor = LLMChainExtractor.from_llm(llm)
compression_retriever = ContextualCompressionRetriever(base_compressor=compressor, base_retriever=retriever)

compressed_docs = compression_retriever.get_relevant_documents("What did the president say about Ketanji Jackson Brown")
pretty_print_docs(compressed_docs)
    Document 1:
    
    "One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court. 
    
    And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson. One of our nation’s top legal minds, who will continue Justice Breyer’s legacy of excellence."
    ----------------------------------------------------------------------------------------------------
    Document 2:
    
    "A former top litigator in private practice. A former federal public defender. And from a family of public school educators and police officers. A consensus builder. Since she’s been nominated, she’s received a broad range of support—from the Fraternal Order of Police to former judges appointed by Democrats and Republicans."

更多内置压缩器：过滤器​

LLMChainFilter​

LLMChainFilter 是一个稍微简单但更健壮的压缩器，它使用 LLM 链来决定哪些最初检索到的文档要被过滤掉，哪些要返回，而无需操作文档内容。

from langchain.retrievers.document_compressors import LLMChainFilter

_filter = LLMChainFilter.from_llm(llm)
compression_retriever = ContextualCompressionRetriever(base_compressor=_filter, base_retriever=retriever)

compressed_docs = compression_retriever.get_relevant_documents("What did the president say about Ketanji Jackson Brown")
pretty_print_docs(compressed_docs)
    Document 1:
    
    Tonight. I call on the Senate to: Pass the Freedom to Vote Act. Pass the John Lewis Voting Rights Act. And while you’re at it, pass the Disclose Act so Americans can know who is funding our elections. 
    
    Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service. 
    
    One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court. 
    
    And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson. One of our nation’s top legal minds, who will continue Justice Breyer’s legacy of excellence.

EmbeddingsFilter​

对每个检索到的文档进行额外的 LLM 调用是昂贵且缓慢的。EmbeddingsFilter 提供了一种更便宜且更快速的选择，它通过嵌入文档和查询，只返回与查询具有足够相似嵌入的文档。

from langchain.embeddings import OpenAIEmbeddings
from langchain.retrievers.document_compressors import EmbeddingsFilter

embeddings = OpenAIEmbeddings()
embeddings_filter = EmbeddingsFilter(embeddings=embeddings, similarity_threshold=0.76)
compression_retriever = ContextualCompressionRetriever(base_compressor=embeddings_filter, base_retriever=retriever)

compressed_docs = compression_retriever.get_relevant_documents("What did the president say about Ketanji Jackson Brown")
pretty_print_docs(compressed_docs)
    Document 1:
    
    Tonight. I call on the Senate to: Pass the Freedom to Vote Act. Pass the John Lewis Voting Rights Act. And while you’re at it, pass the Disclose Act so Americans can know who is funding our elections. 
    
    Tonight, I’d like to honor someone who has dedicated his life to serve this country: Justice Stephen Breyer—an Army veteran, Constitutional scholar, and retiring Justice of the United States Supreme Court. Justice Breyer, thank you for your service. 
    
    One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court. 
    
    And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson. One of our nation’s top legal minds, who will continue Justice Breyer’s legacy of excellence.
    ----------------------------------------------------------------------------------------------------
    Document 2:
    
    A former top litigator in private practice. A former federal public defender. And from a family of public school educators and police officers. A consensus builder. Since she’s been nominated, she’s received a broad range of support—from the Fraternal Order of Police to former judges appointed by Democrats and Republicans. 
    
    And if we are to advance liberty and justice, we need to secure the Border and fix the immigration system. 
    
    We can do both. At our border, we’ve installed new technology like cutting-edge scanners to better detect drug smuggling.  
    
    We’ve set up joint patrols with Mexico and Guatemala to catch more human traffickers.  
    
    We’re putting in place dedicated immigration judges so families fleeing persecution and violence can have their cases heard faster. 
    
    We’re securing commitments and supporting partners in South and Central America to host more refugees and secure their own borders.
    ----------------------------------------------------------------------------------------------------
    Document 3:
    
    And for our LGBTQ+ Americans, let’s finally get the bipartisan Equality Act to my desk. The onslaught of state laws targeting transgender Americans and their families is wrong. 
    
    As I said last year, especially to our younger transgender Americans, I will always have your back as your President, so you can be yourself and reach your God-given potential. 
    
    While it often appears that we never agree, that isn’t true. I signed 80 bipartisan bills into law last year. From preventing government shutdowns to protecting Asian-Americans from still-too-common hate crimes to reforming military justice. 
    
    And soon, we’ll strengthen the Violence Against Women Act that I first wrote three decades ago. It is important for us to show the nation that we can come together and do big things. 
    
    So tonight I’m offering a Unity Agenda for the Nation. Four big things we can do together.  
    
    First, beat the opioid epidemic.

将压缩器和文档转换器串联起来

使用 DocumentCompressorPipeline 我们还可以轻松地将多个压缩器按顺序组合起来。除了压缩器，我们还可以将 BaseDocumentTransformer 添加到我们的管道中，它们不执行任何上下文压缩，只是在一组文档上执行一些转换。例如，TextSplitter 可以用作文档转换器，将文档分割成较小的片段，而 EmbeddingsRedundantFilter 可以基于文档之间的嵌入相似性过滤掉冗余文档。

下面，我们通过首先将文档分割成较小的块，然后删除冗余文档，最后根据与查询的相关性进行过滤，创建了一个压缩器管道。

from langchain.document_transformers import EmbeddingsRedundantFilter
from langchain.retrievers.document_compressors import DocumentCompressorPipeline
from langchain.text_splitter import CharacterTextSplitter

splitter = CharacterTextSplitter(chunk_size=300, chunk_overlap=0, separator=". ")
redundant_filter = EmbeddingsRedundantFilter(embeddings=embeddings)
relevant_filter = EmbeddingsFilter(embeddings=embeddings, similarity_threshold=0.76)
pipeline_compressor = DocumentCompressorPipeline(
    transformers=[splitter, redundant_filter, relevant_filter]
)
compression_retriever = ContextualCompressionRetriever(base_compressor=pipeline_compressor, base_retriever=retriever)

compressed_docs = compression_retriever.get_relevant_documents("What did the president say about Ketanji Jackson Brown")
pretty_print_docs(compressed_docs)
    Document 1:
    
    One of the most serious constitutional responsibilities a President has is nominating someone to serve on the United States Supreme Court. 
    
    And I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson
    ----------------------------------------------------------------------------------------------------
    Document 2:
    
    As I said last year, especially to our younger transgender Americans, I will always have your back as your President, so you can be yourself and reach your God-given potential. 
    
    While it often appears that we never agree, that isn’t true. I signed 80 bipartisan bills into law last year
    ----------------------------------------------------------------------------------------------------
    Document 3:
    
    A former top litigator in private practice. A former federal public defender. And from a family of public school educators and police officers. A consensus builder