DocumentPreprocessor

A SuperComponent that splits and cleans documents in a single step. It combines DocumentSplitter and DocumentCleaner into one component for use in indexing pipelines.

Key Features

• Splits documents into smaller chunks using configurable units such as words, sentences, pages, or paragraphs.
• Cleans documents by removing empty lines, extra whitespaces, and repeated substrings like headers and footers.
• Supports overlapping splits to preserve context across chunks.
• Respects sentence boundaries when splitting by word.
• Supports custom splitting functions.

Configuration

1. Drag the DocumentPreprocessor component onto the canvas from the Component Library.
2. Click on the component to open the configuration panel.
3. Configure the component settings:
   • Choose a Split By unit: word, sentence, passage, page, line, or function.
   • Set Split Length to the maximum number of units in each chunk.
   • Set Split Overlap to the number of overlapping units between consecutive chunks.
   • Toggle Remove Empty Lines to remove empty lines from the document.
   • Toggle Remove Extra Whitespaces to remove extra whitespaces.
   • Set Split Threshold to define the minimum number of units per chunk. Chunks smaller than this threshold are merged with the previous chunk.
   • Toggle Respect Sentence Boundary to avoid splitting in the middle of a sentence when splitting by word.
   • Set Language for the NLTK sentence tokenizer (default: en).
   • Toggle Remove Repeated Substrings to remove repeated headers and footers across pages.
   • Toggle Keep ID to retain the original document IDs.
   • Set Remove Substrings to specify a list of strings to remove.
   • Set Remove Regex to specify a regular expression pattern whose matches are removed.
   • Set Unicode Normalization to apply Unicode normalization.
   • Toggle ASCII Only to convert text to ASCII only.

Connections

DocumentPreprocessor accepts a list of Document objects and outputs processed Document objects.

It's typically used in indexes between a document converter and a document embedder, or before DocumentWriter.

Source Code

To check this component's source code, open document_preprocessor.py in the Haystack repository.

Usage Examples

Basic Configuration

  DocumentPreprocessor:
    type: haystack.components.preprocessors.document_preprocessor.DocumentPreprocessor
    init_parameters:
      split_by: word
      split_length: 200
      split_overlap: 30
      respect_sentence_boundary: true
      language: en
      remove_empty_lines: true
      remove_extra_whitespaces: true
      remove_repeated_substrings: false

In an Index

This index pipeline uses DocumentPreprocessor to split and clean documents before embedding and writing them to a Document Store:

# haystack-pipeline
components:
  MultiFileConverter:
    type: haystack.components.converters.multi_file_converter.MultiFileConverter
    init_parameters:
      encoding: utf-8

  DocumentPreprocessor:
    type: haystack.components.preprocessors.document_preprocessor.DocumentPreprocessor
    init_parameters:
      split_by: word
      split_length: 200
      split_overlap: 30
      respect_sentence_boundary: true
      language: en
      remove_empty_lines: true
      remove_extra_whitespaces: true
      remove_repeated_substrings: false

  SentenceTransformersDocumentEmbedder:
    type: haystack_integrations.components.embedders.sentence_transformers.SentenceTransformersDocumentEmbedder
    init_parameters:
      model: intfloat/e5-base-v2
      normalize_embeddings: true

  DocumentWriter:
    type: haystack.components.writers.document_writer.DocumentWriter
    init_parameters:
      policy: OVERWRITE
      document_store:
        type: haystack_integrations.document_stores.opensearch.document_store.OpenSearchDocumentStore
        init_parameters:
          hosts:
          index: ''
          embedding_dim: 768
          create_index: true

connections:
  - sender: MultiFileConverter.documents
    receiver: DocumentPreprocessor.documents
  - sender: DocumentPreprocessor.documents
    receiver: SentenceTransformersDocumentEmbedder.documents
  - sender: SentenceTransformersDocumentEmbedder.documents
    receiver: DocumentWriter.documents

max_runs_per_component: 100

inputs:
  files:
    - MultiFileConverter.sources

In this example:

1. MultiFileConverter converts uploaded files into documents.
2. DocumentPreprocessor splits documents into chunks of 200 words with 30-word overlap, respecting sentence boundaries. It also removes empty lines and extra whitespace.
3. SentenceTransformersDocumentEmbedder generates embeddings for the processed documents.
4. DocumentWriter writes the embedded documents to OpenSearch.

Parameters

Inputs

Parameter	Type	Description
documents	List[Document]	Documents to process.

Outputs

Parameter	Type	Description
documents	List[Document]	Processed list of documents.

Init Parameters

These are the parameters you can configure in Pipeline Builder:

Splitter Parameters:

Parameter	Type	Default	Description
split_by	Literal['function', 'page', 'passage', 'period', 'word', 'line', 'sentence']	word	The unit of splitting.
split_length	int	250	The maximum number of units (words, lines, pages, and so on) in each split.
split_overlap	int	0	The number of overlapping units between consecutive splits.
split_threshold	int	0	The minimum number of units per split. If a split is smaller, it's merged with the previous split.
splitting_function	Optional[Callable]	None	A custom function for splitting if split_by="function".
respect_sentence_boundary	bool	False	If True, splits by words but tries not to break inside a sentence.
language	str	en	Language used by the sentence tokenizer.
use_split_rules	bool	True	Whether to apply additional splitting heuristics for the sentence splitter.
extend_abbreviations	bool	True	Whether to extend the sentence splitter with curated abbreviations for certain languages.

Cleaner Parameters:

Parameter	Type	Default	Description
remove_empty_lines	bool	True	If True, removes empty lines.
remove_extra_whitespaces	bool	True	If True, removes extra whitespaces.
remove_repeated_substrings	bool	False	If True, removes repeated substrings like headers/footers across pages.
keep_id	bool	False	If True, keeps the original document IDs.
remove_substrings	Optional[List[str]]	None	A list of strings to remove from the document content.
remove_regex	Optional[str]	None	A regex pattern whose matches are removed from the document content.
unicode_normalization	Optional[Literal['NFC', 'NFKC', 'NFD', 'NFKD']]	None	Unicode normalization form to apply to the text.
ascii_only	bool	False	If True, converts text to ASCII only.

Run Method Parameters

These are the parameters you can configure for the component's run() method. This means you can pass these parameters at query time through the API, in Playground, or when running a job. For details, see Modify Pipeline Parameters at Query Time.

Parameter	Type	Description
documents	List[Document]	Documents to process.

Related Information

• DocumentCleaner
• DocumentSplitter
• Pipeline Components