深入浅出 langchain 3. TextSplitter&DocumentLoader

Carota不是菜
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上节有说到如何通过Vecstore 来进行存储数据与检索数据, 那么这节讲一下数据的加载与处理 DocumentLoader 负责加载数据, 我们平常接触的数据格式有各种各样的(markdown, pdf, txt 等等), 将格式各样的文件内容加载到程序中, 存储以文本 TextSplitter 就是负责如何解析这些文本的

Document Loader

先给出一个简单的代码示例来分析如何使用

from langchain_community.document_loaders import UnstructuredHTMLLoader

loader = UnstructuredHTMLLoader("example_data/fake-content.html")
data = loader.load()

data

输出结果

[Document(page_content='My First Heading\n\nMy first paragraph.', lookup_str='', metadata={'source': 'example_data/fake-content.html'}, lookup_index=0)]

代码逻辑就是读取 html 文件, 加载进来

TextSplitter

对于 Html 这种结构化的数据, 我们可以按照结构的语义分组

from langchain_text_splitters import HTMLHeaderTextSplitter

html_string = """
<!DOCTYPE html>
<html>
<body>
    <div>
        <h1>Foo</h1>
        <p>Some intro text about Foo.</p>
        <div>
            <h2>Bar main section</h2>
            <p>Some intro text about Bar.</p>
            <h3>Bar subsection 1</h3>
            <p>Some text about the first subtopic of Bar.</p>
            <h3>Bar subsection 2</h3>
            <p>Some text about the second subtopic of Bar.</p>
        </div>
        <div>
            <h2>Baz</h2>
            <p>Some text about Baz</p>
        </div>
        <br>
        <p>Some concluding text about Foo</p>
    </div>
</body>
</html>
"""

headers_to_split_on = [
    ("h1", "Header 1"),
    ("h2", "Header 2"),
    ("h3", "Header 3"),
]

html_splitter = HTMLHeaderTextSplitter(headers_to_split_on=headers_to_split_on)
html_header_splits = html_splitter.split_text(html_string)
html_header_splits

输出结果

[Document(page_content='Foo'), Document(page_content='Some intro text about Foo.  \nBar main section Bar subsection 1 Bar subsection 2', metadata={'Header 1': 'Foo'}), Document(page_content='Some intro text about Bar.', metadata={'Header 1': 'Foo', 'Header 2': 'Bar main section'}), Document(page_content='Some text about the first subtopic of Bar.', metadata={'Header 1': 'Foo', 'Header 2': 'Bar main section', 'Header 3': 'Bar subsection 1'}), Document(page_content='Some text about the second subtopic of Bar.', metadata={'Header 1': 'Foo', 'Header 2': 'Bar main section', 'Header 3': 'Bar subsection 2'}), Document(page_content='Baz', metadata={'Header 1': 'Foo'}), Document(page_content='Some text about Baz', metadata={'Header 1': 'Foo', 'Header 2': 'Baz'}), Document(page_content='Some concluding text about Foo', metadata={'Header 1': 'Foo'})]

可以看到上面输出的内容是Document, 其实和 DocumentLoader 加载出来的对象一致. 那么就意味着其实 TextSplitter 是一个可以进行链式处理的操作类

from langchain_text_splitters import RecursiveCharacterTextSplitter

url = "https://plato.stanford.edu/entries/goedel/"

headers_to_split_on = [
    ("h1", "Header 1"),
    ("h2", "Header 2"),
    ("h3", "Header 3"),
    ("h4", "Header 4"),
]

html_splitter = HTMLHeaderTextSplitter(headers_to_split_on=headers_to_split_on)

# for local file use html_splitter.split_text_from_file(<path_to_file>)
html_header_splits = html_splitter.split_text_from_url(url)

chunk_size = 500
chunk_overlap = 30
text_splitter = RecursiveCharacterTextSplitter(
    chunk_size=chunk_size, chunk_overlap=chunk_overlap
)

# Split
splits = text_splitter.split_documents(html_header_splits)
splits[80:85]

输出结果

[Document(page_content='We see that Gödel first tried to reduce the consistency problem for analysis to that of arithmetic. This seemed to require a truth definition for arithmetic, which in turn led to paradoxes, such as the Liar paradox (“This sentence is false”) and Berry’s paradox (“The least number not defined by an expression consisting of just fourteen English words”). Gödel then noticed that such paradoxes would not necessarily arise if truth were replaced by provability. But this means that arithmetic truth', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='means that arithmetic truth and arithmetic provability are not co-extensive — whence the First Incompleteness Theorem.', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='This account of Gödel’s discovery was told to Hao Wang very much after the fact; but in Gödel’s contemporary correspondence with Bernays and Zermelo, essentially the same description of his path to the theorems is given. (See Gödel 2003a and Gödel 2003b respectively.) From those accounts we see that the undefinability of truth in arithmetic, a result credited to Tarski, was likely obtained in some form by Gödel by 1931. But he neither publicized nor published the result; the biases logicians', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='result; the biases logicians had expressed at the time concerning the notion of truth, biases which came vehemently to the fore when Tarski announced his results on the undefinability of truth in formal systems 1935, may have served as a deterrent to Gödel’s publication of that theorem.', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='We now describe the proof of the two theorems, formulating Gödel’s results in Peano arithmetic. Gödel himself used a system related to that defined in Principia Mathematica, but containing Peano arithmetic. In our presentation of the First and Second Incompleteness Theorems we refer to Peano arithmetic as P, following Gödel’s notation.', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.2 The proof of the First Incompleteness Theorem'})]

上述的例子就可以发现, 从HTMLHeaderTextSplitter处理完成的内容后还可以通过RecursiveCharacterTextSplitter进一步进行处理.

总结

以上第二章和第三章的内容就是整体 Retrieval 的主要概念.

简单一句话总结, Retrieval就是为了检索高度关联的内容而设计的, 其实就是为了补足 LLM 大模型预设数据缺失的问题.

在某些垂直领域, 检索数据的质量, 对于大模型的使用效果也是有很大的影响

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