如何基于语义相似性分割文本

源自格雷格·卡姆拉特精彩笔记： 5_文本分割的五个层级

所有功劳都归于他。

本指南介绍如何根据语义相似性来拆分文本块。如果嵌入向量之间的距离足够远，就会进行拆分。

从高层次上看，这会将文本拆分为句子，然后每3个句子为一组进行分组，接着合并嵌入空间中相似的句子。

安装依赖项

!pip install --quiet langchain_experimental langchain_openai

加载示例数据

# This is a long document we can split up.
with open("state_of_the_union.txt") as f:
    state_of_the_union = f.read()

创建文本分割器

要实例化一个 SemanticChunker，我们必须指定一个嵌入模型。下面我们将使用 OpenAIEmbeddings。

from langchain_experimental.text_splitter import SemanticChunker
from langchain_openai.embeddings import OpenAIEmbeddings

text_splitter = SemanticChunker(OpenAIEmbeddings())

API 参考：SemanticChunker | OpenAIEmbeddings

拆分文本

我们以常规方式拆分文本，例如通过调用 .create_documents 来创建 LangChain Document 对象：

docs = text_splitter.create_documents([state_of_the_union])
print(docs[0].page_content)

Madam Speaker, Madam Vice President, our First Lady and Second Gentleman. Members of Congress and the Cabinet. Justices of the Supreme Court. My fellow Americans. Last year COVID-19 kept us apart. This year we are finally together again. Tonight, we meet as Democrats Republicans and Independents. But most importantly as Americans. With a duty to one another to the American people to the Constitution. And with an unwavering resolve that freedom will always triumph over tyranny. Six days ago, Russia’s Vladimir Putin sought to shake the foundations of the free world thinking he could make it bend to his menacing ways. But he badly miscalculated. He thought he could roll into Ukraine and the world would roll over. Instead he met a wall of strength he never imagined. He met the Ukrainian people. From President Zelenskyy to every Ukrainian, their fearlessness, their courage, their determination, inspires the world. Groups of citizens blocking tanks with their bodies. Everyone from students to retirees teachers turned soldiers defending their homeland. In this struggle as President Zelenskyy said in his speech to the European Parliament “Light will win over darkness.” The Ukrainian Ambassador to the United States is here tonight. Let each of us here tonight in this Chamber send an unmistakable signal to Ukraine and to the world. Please rise if you are able and show that, Yes, we the United States of America stand with the Ukrainian people. Throughout our history we’ve learned this lesson when dictators do not pay a price for their aggression they cause more chaos. They keep moving.

断点

此分块器通过判断何时“拆分”句子来工作。它是通过查找任意两个句子之间的嵌入差异来实现的。当该差异超过某个阈值时，句子就会被拆分。

确定该阈值的方法有几种，这些方法由 breakpoint_threshold_type 关键字参数控制。

注意：如果生成的块大小过小或过大，可以使用额外的参数 breakpoint_threshold_amount 和 min_chunk_size 进行调整。

百分位数

默认的分割方式是基于百分位数。在此方法中，会计算所有句子之间的差异，然后将大于X百分位数的差异处进行分割。X的默认值为95.0，可通过关键字参数breakpoint_threshold_amount进行调整，该参数期望一个介于0.0到100.0之间的数值。

text_splitter = SemanticChunker(
    OpenAIEmbeddings(), breakpoint_threshold_type="percentile"
)

docs = text_splitter.create_documents([state_of_the_union])
print(docs[0].page_content)

Madam Speaker, Madam Vice President, our First Lady and Second Gentleman. Members of Congress and the Cabinet. Justices of the Supreme Court. My fellow Americans. Last year COVID-19 kept us apart. This year we are finally together again. Tonight, we meet as Democrats Republicans and Independents. But most importantly as Americans. With a duty to one another to the American people to the Constitution. And with an unwavering resolve that freedom will always triumph over tyranny. Six days ago, Russia’s Vladimir Putin sought to shake the foundations of the free world thinking he could make it bend to his menacing ways. But he badly miscalculated. He thought he could roll into Ukraine and the world would roll over. Instead he met a wall of strength he never imagined. He met the Ukrainian people. From President Zelenskyy to every Ukrainian, their fearlessness, their courage, their determination, inspires the world. Groups of citizens blocking tanks with their bodies. Everyone from students to retirees teachers turned soldiers defending their homeland. In this struggle as President Zelenskyy said in his speech to the European Parliament “Light will win over darkness.” The Ukrainian Ambassador to the United States is here tonight. Let each of us here tonight in this Chamber send an unmistakable signal to Ukraine and to the world. Please rise if you are able and show that, Yes, we the United States of America stand with the Ukrainian people. Throughout our history we’ve learned this lesson when dictators do not pay a price for their aggression they cause more chaos. They keep moving.

print(len(docs))

26

标准差

在此方法中，任何大于 X 个标准差的差异都会被分割。X 的默认值为 3.0，可以通过关键字参数 breakpoint_threshold_amount 进行调整。

text_splitter = SemanticChunker(
    OpenAIEmbeddings(), breakpoint_threshold_type="standard_deviation"
)

docs = text_splitter.create_documents([state_of_the_union])
print(docs[0].page_content)

Madam Speaker, Madam Vice President, our First Lady and Second Gentleman. Members of Congress and the Cabinet. Justices of the Supreme Court. My fellow Americans. Last year COVID-19 kept us apart. This year we are finally together again. Tonight, we meet as Democrats Republicans and Independents. But most importantly as Americans. With a duty to one another to the American people to the Constitution. And with an unwavering resolve that freedom will always triumph over tyranny. Six days ago, Russia’s Vladimir Putin sought to shake the foundations of the free world thinking he could make it bend to his menacing ways. But he badly miscalculated. He thought he could roll into Ukraine and the world would roll over. Instead he met a wall of strength he never imagined. He met the Ukrainian people. From President Zelenskyy to every Ukrainian, their fearlessness, their courage, their determination, inspires the world. Groups of citizens blocking tanks with their bodies. Everyone from students to retirees teachers turned soldiers defending their homeland. In this struggle as President Zelenskyy said in his speech to the European Parliament “Light will win over darkness.” The Ukrainian Ambassador to the United States is here tonight. Let each of us here tonight in this Chamber send an unmistakable signal to Ukraine and to the world. Please rise if you are able and show that, Yes, we the United States of America stand with the Ukrainian people. Throughout our history we’ve learned this lesson when dictators do not pay a price for their aggression they cause more chaos. They keep moving. And the costs and the threats to America and the world keep rising. That’s why the NATO Alliance was created to secure peace and stability in Europe after World War 2. The United States is a member along with 29 other nations. It matters. American diplomacy matters. American resolve matters. Putin’s latest attack on Ukraine was premeditated and unprovoked. He rejected repeated efforts at diplomacy. He thought the West and NATO wouldn’t respond. And he thought he could divide us at home. Putin was wrong. We were ready. Here is what we did. We prepared extensively and carefully. We spent months building a coalition of other freedom-loving nations from Europe and the Americas to Asia and Africa to confront Putin. I spent countless hours unifying our European allies. We shared with the world in advance what we knew Putin was planning and precisely how he would try to falsely justify his aggression. We countered Russia’s lies with truth. And now that he has acted the free world is holding him accountable. Along with twenty-seven members of the European Union including France, Germany, Italy, as well as countries like the United Kingdom, Canada, Japan, Korea, Australia, New Zealand, and many others, even Switzerland. We are inflicting pain on Russia and supporting the people of Ukraine. Putin is now isolated from the world more than ever. Together with our allies –we are right now enforcing powerful economic sanctions. We are cutting off Russia’s largest banks from the international financial system. Preventing Russia’s central bank from defending the Russian Ruble making Putin’s $630 Billion “war fund” worthless. We are choking off Russia’s access to technology that will sap its economic strength and weaken its military for years to come. Tonight I say to the Russian oligarchs and corrupt leaders who have bilked billions of dollars off this violent regime no more. The U.S. Department of Justice is assembling a dedicated task force to go after the crimes of Russian oligarchs. We are joining with our European allies to find and seize your yachts your luxury apartments your private jets. We are coming for your ill-begotten gains. And tonight I am announcing that we will join our allies in closing off American air space to all Russian flights – further isolating Russia – and adding an additional squeeze –on their economy. The Ruble has lost 30% of its value. The Russian stock market has lost 40% of its value and trading remains suspended. Russia’s economy is reeling and Putin alone is to blame. Together with our allies we are providing support to the Ukraini