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许多聊天或问答应用程序都涉及在嵌入和向量存储之前对输入文档进行分块。 Pinecone 的这些笔记提供了一些有用的提示：
When a full paragraph or document is embedded, the embedding process considers both the overall context and the relationships between the sentences and phrases within the text. This can result in a more comprehensive vector representation that captures the broader meaning and themes of the text.
如前所述，分块通常旨在将具有共同上下文的文本保持在一起。考虑到这一点，我们可能希望特别尊重文档本身的结构。例如，Markdown 文件按标题组织。在特定标题组内创建块是一个直观的想法。为了解决这个挑战，我们可以使用 MarkdownHeaderTextSplitter。这将根据一组指定的标题来分割 Markdown 文件。 例如，如果我们想分割此 Markdown：
md = '# Foo\n\n ## Bar\n\nHi this is Jim  \nHi this is Joe\n\n ## Baz\n\n Hi this is Molly'
我们可以指定要分割的标题 
[("#", "Header 1"),("##", "Header 2")]
内容按共同标题分组或分割 
{'content': 'Hi this is Jim  \nHi this is Joe', 'metadata': {'Header 1': 'Foo', 'Header 2': 'Bar'}}
{'content': 'Hi this is Molly', 'metadata': {'Header 1': 'Foo', 'Header 2': 'Baz'}}
让我们看看下面的一些例子。

​
基本用法

pip install -qU langchain-text-splitters

from langchain_text_splitters import MarkdownHeaderTextSplitter

markdown_document = "# Foo\n\n    ## Bar\n\nHi this is Jim\n\nHi this is Joe\n\n ### Boo \n\n Hi this is Lance \n\n ## Baz\n\n Hi this is Molly"

headers_to_split_on = [
    ("#", "Header 1"),
    ("##", "Header 2"),
    ("###", "Header 3"),
]

markdown_splitter = MarkdownHeaderTextSplitter(headers_to_split_on)
md_header_splits = markdown_splitter.split_text(markdown_document)
md_header_splits

[Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar'}, page_content='Hi this is Jim  \nHi this is Joe'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar', 'Header 3': 'Boo'}, page_content='Hi this is Lance'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Baz'}, page_content='Hi this is Molly')]

type(md_header_splits[0])

langchain_core.documents.base.Document
默认情况下，`MarkdownHeaderTextSplitter` 会从输出块的内容中剥离正在分割的标题。这可以通过设置 `strip_headers = False` 来禁用。 
markdown_splitter = MarkdownHeaderTextSplitter(headers_to_split_on, strip_headers=False)
md_header_splits = markdown_splitter.split_text(markdown_document)
md_header_splits

[Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar'}, page_content='# Foo  \n## Bar  \nHi this is Jim  \nHi this is Joe'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar', 'Header 3': 'Boo'}, page_content='### Boo  \nHi this is Lance'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Baz'}, page_content='## Baz  \nHi this is Molly')]
默认的 `MarkdownHeaderTextSplitter` 会去除空格和换行符。要保留 Markdown 文档的原始格式，请查看 `ExperimentalMarkdownSyntaxTextSplitter`。

​
如何将 Markdown 行作为单独的文档返回

默认情况下，`MarkdownHeaderTextSplitter` 会根据 `headers_to_split_on` 中指定的标题聚合行。我们可以通过指定 `return_each_line` 来禁用此功能。 
markdown_splitter = MarkdownHeaderTextSplitter(
    headers_to_split_on,
    return_each_line=True,
)
md_header_splits = markdown_splitter.split_text(markdown_document)
md_header_splits

[Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar'}, page_content='Hi this is Jim'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar'}, page_content='Hi this is Joe'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Bar', 'Header 3': 'Boo'}, page_content='Hi this is Lance'),
 Document(metadata={'Header 1': 'Foo', 'Header 2': 'Baz'}, page_content='Hi this is Molly')]
请注意，此处标题信息保留在每个文档的 `metadata` 中。

​
如何限制块大小

在每个 markdown 组中，我们可以应用任何我们想要的文本分割器，例如 `RecursiveCharacterTextSplitter`，它允许进一步控制块大小。 
markdown_document = "# Intro \n\n    ## History \n\n Markdown[9] is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber created Markdown in 2004 as a markup language that is appealing to human readers in its source code form.[9] \n\n Markdown is widely used in blogging, instant messaging, online forums, collaborative software, documentation pages, and readme files. \n\n ## Rise and divergence \n\n As Markdown popularity grew rapidly, many Markdown implementations appeared, driven mostly by the need for \n\n additional features such as tables, footnotes, definition lists,[note 1] and Markdown inside HTML blocks. \n\n #### Standardization \n\n From 2012, a group of people, including Jeff Atwood and John MacFarlane, launched what Atwood characterised as a standardisation effort. \n\n ## Implementations \n\n Implementations of Markdown are available for over a dozen programming languages."

headers_to_split_on = [
    ("#", "Header 1"),
    ("##", "Header 2"),
]

# MD splits
markdown_splitter = MarkdownHeaderTextSplitter(
    headers_to_split_on=headers_to_split_on, strip_headers=False
)
md_header_splits = markdown_splitter.split_text(markdown_document)

# Char-level splits
from langchain_text_splitters import RecursiveCharacterTextSplitter

chunk_size = 250
chunk_overlap = 30
text_splitter = RecursiveCharacterTextSplitter(
    chunk_size=chunk_size, chunk_overlap=chunk_overlap
)

# Split
splits = text_splitter.split_documents(md_header_splits)
splits

[Document(metadata={'Header 1': 'Intro', 'Header 2': 'History'}, page_content='# Intro  \n## History  \nMarkdown[9] is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber created Markdown in 2004 as a markup language that is appealing to human readers in its source code form.[9]'),
 Document(metadata={'Header 1': 'Intro', 'Header 2': 'History'}, page_content='Markdown is widely used in blogging, instant messaging, online forums, collaborative software, documentation pages, and readme files.'),
 Document(metadata={'Header 1': 'Intro', 'Header 2': 'Rise and divergence'}, page_content='## Rise and divergence  \nAs Markdown popularity grew rapidly, many Markdown implementations appeared, driven mostly by the need for  \nadditional features such as tables, footnotes, definition lists,[note 1] and Markdown inside HTML blocks.'),
 Document(metadata={'Header 1': 'Intro', 'Header 2': 'Rise and divergence'}, page_content='#### Standardization  \nFrom 2012, a group of people, including Jeff Atwood and John MacFarlane, launched what Atwood characterised as a standardisation effort.'),
 Document(metadata={'Header 1': 'Intro', 'Header 2': 'Implementations'}, page_content='## Implementations  \nImplementations of Markdown are available for over a dozen programming languages.')]

​
故障排除：`chunk_overlap` 似乎不适用

  • 在基于标题的分割（例如 `MarkdownHeaderTextSplitter`）之后，使用 **`split_documents(docs)`**（而不是 `split_text`），以便在**每个部分内**应用重叠，并且每个部分的元数据（标题）保留在块上。
  • 仅当**单个部分**超出 `chunk_size` 并被分割成多个块时，才会出现重叠。
  • 重叠**不会跨越**节/文档边界（例如，`# H1` → `## H2`）。
  • 如果标题变成了一个微小的第一个块，请考虑将 `strip_headers` 设置为 `True`，这样标题行就不会成为一个独立的块。
  • 如果您的文本缺少换行符/空格，请在 `separators` 中保留一个备用的 `""`，以便分割器仍能分割并应用重叠。
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