如何使用上下文压缩进行检索
检索的一个挑战是，通常在将数据摄取到系统中时，您不知道文档存储系统将面临哪些特定查询。这意味着与查询最相关的資訊可能隐藏在一个包含大量无关文本的文档中。将整个文档传递到您的应用程序可能会导致更昂贵的 LLM 调用和更差的响应。
上下文压缩旨在解决这个问题。其理念很简单：不是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，以便仅返回相关資訊。“压缩”在这里指的是压缩单个文档的内容，以及过滤掉整个文档。
要使用上下文压缩检索器，您需要
- 一个基本检索器
- 一个文档压缩器
上下文压缩检索器将查询传递给基本检索器，获取初始文档并将其传递给文档压缩器。文档压缩器接收一系列文档，通过减少文档内容或完全删除文档来缩短该序列。
入门
# 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)]
)
)
使用普通向量存储检索器
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（分块）开始。我们可以看到，给定一个示例问题，我们的检索器会返回一个或两个相关的文档，以及一些不相关的文档。即使是相关的文档也包含很多不相关的信息。
from langchain_community.document_loaders import TextLoader
from langchain_community.vectorstores import FAISS
from langchain_openai import OpenAIEmbeddings
from langchain_text_splitters import CharacterTextSplitter
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.invoke("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.
使用 LLMChainExtractor 添加上下文压缩
现在让我们用 ContextualCompressionRetriever 包装我们的基础检索器。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部分内容。
from langchain.retrievers import ContextualCompressionRetriever
from langchain.retrievers.document_compressors import LLMChainExtractor
from langchain_openai import OpenAI
llm = OpenAI(temperature=0)
compressor = LLMChainExtractor.from_llm(llm)
compression_retriever = ContextualCompressionRetriever(
base_compressor=compressor, base_retriever=retriever
)
compressed_docs = compression_retriever.invoke(
"What did the president say about Ketanji Jackson Brown"
)
pretty_print_docs(compressed_docs)
Document 1:
I did that 4 days ago, when I nominated Circuit Court of Appeals Judge Ketanji Brown Jackson.
更多内置压缩器：过滤器
LLMChainFilter
LLMChainFilter 是一个稍微简单但更强大的压缩器，它使用 LLM 链来决定过滤掉哪些初始检索的文档，以及返回哪些文档，而不会改变文档内容。
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.invoke(
"What did the president say about Ketanji Jackson Brown"
)
pretty_print_docs(compressed_docs)
API 参考：LLMChainFilter
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.
LLMListwiseRerank
LLMListwiseRerank 使用 零样本列表式文档重新排序，功能与 LLMChainFilter 类似，是一个更强大但更昂贵的选择。建议使用更强大的 LLM。
请注意，LLMListwiseRerank 需要一个已实现 with_structured_output 方法的模型。
from langchain.retrievers.document_compressors import LLMListwiseRerank
from langchain_openai import ChatOpenAI
llm = ChatOpenAI(model="gpt-4o-mini", temperature=0)
_filter = LLMListwiseRerank.from_llm(llm, top_n=1)
compression_retriever = ContextualCompressionRetriever(
base_compressor=_filter, base_retriever=retriever
)
compressed_docs = compression_retriever.invoke(
"What did the president say about Ketanji Jackson Brown"
)
pretty_print_docs(compressed_docs)
API 参考：LLMListwiseRerank | ChatOpenAI
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
对每个检索的文档进行额外的 LLM 调用既昂贵又慢。EmbeddingsFilter 通过嵌入文档和查询，仅返回那些与查询具有足够相似嵌入的文档，提供了一个更便宜、更快的选择。
from langchain.retrievers.document_compressors import EmbeddingsFilter
from langchain_openai import OpenAIEmbeddings
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.invoke(
"What did the president say about Ketanji Jackson Brown"
)
pretty_print_docs(compressed_docs)
API 参考：EmbeddingsFilter | OpenAIEmbeddings
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.
将压缩器和文档转换器串联在一起
使用 DocumentCompressorPipeline，我们也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，这些转换器不执行任何上下文压缩，而是对一组文档执行一些转换。例如，TextSplitter 可以用作文档转换器，将文档拆分成更小的片段，而 EmbeddingsRedundantFilter 可以用来根据文档之间的嵌入相似性过滤掉冗余文档。
下面，我们首先将文档拆分成更小的块，然后删除冗余文档，最后根据与查询的相关性进行过滤，从而创建了一个压缩器管道。
from langchain.retrievers.document_compressors import DocumentCompressorPipeline
from langchain_community.document_transformers import EmbeddingsRedundantFilter
from langchain_text_splitters 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.invoke(
"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
----------------------------------------------------------------------------------------------------
Document 4:
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