---
license: mit
task_categories:
- text-generation
- text-classification
- token-classification
- question-answering
- zero-shot-classification
- summarization
- feature-extraction
- fill-mask
- sentence-similarity
language:
- en
tags:
- NLP
pretty_name: bookcorpus
size_categories:
- 10M<n<100M
---

# BookCorpus — Cleaned for Pre-training LLMs

A cleaned, deduplicated, document-segmented version of
[`SamuelYang/bookcorpus`](https://huggingface.co/datasets/SamuelYang/bookcorpus)

## TL;DR

| Property | Value |
|---|---|
| Rows (sentences) | **33,649,142** |
| Documents (books) | **4,086** |
| Format | CSV, 3 columns: `doc_id`, `sent_id`, `text` |
| Language | English (lowercased) |
| Source | `SamuelYang/bookcorpus` (74,004,228 raw rows) |

## Schema

| Column | Type | Description |
|---|---|---|
| `doc_id` | int | Inferred document/book identifier. Sentences sharing the same `doc_id` come from the same book. |
| `sent_id` | int | Sentence position within its document (0-indexed). Preserves original order. |
| `text` | string | Cleaned sentence text (lowercased, normalized). |

## How to use it

### Quick load

```python
from datasets import load_dataset

ds = load_dataset("kd13/bookcorpus-clean", split="train")
print(ds[0])
# {'doc_id': 0, 'sent_id': 0, 'text': 'i wish i had a better answer ...'}
```

## Cleaning pipeline

Applied in this order to the source dataset:

1. **Unicode + whitespace normalization** — NFKC normalization, collapse
   consecutive whitespace, strip.
2. **Document segmentation** — since the source is a flat stream of sentences
   without book IDs, document boundaries are inferred from telltale markers
   at the start of books:
   - ISBN lines (e.g. `isbn : 1492913731`)
   - Copyright declarations (`copyright 2013 ...`)
   - `all rights reserved`
   - `chapter 1`
3. **Line-level filters** — sentences are dropped if they:
   - have fewer than **20** or more than **1000** characters
   - match boilerplate patterns (copyright, ISBN, "all rights reserved")
   - have an alphabetic-character ratio below **0.6**
   - have a digit ratio above **0.3**
   - contain no alphabetic characters
4. **Language filter** — cheap English stop-word ratio check (≥ 5% of tokens
   must be in a small English stop-word set; short lines pass through).
5. **Within-document exact dedup** — SHA-1 hashing drops repeated sentences
   inside the same book (e.g. recurring chapter headers, section dividers).
   Note: dedup is *not* applied globally — sentences like "he nodded." occur
   legitimately across many books.
6. **Document filter** — books with fewer than **8** surviving sentences are
   dropped (not enough context for NSP).
7. **Cross-document near-duplicate removal** — a SHA-1 fingerprint of each
   document's first 5 sentences identifies same-book re-uploads; duplicates
   are dropped.

## Cleaning statistics

| Metric | Value |
|---|---|
| Raw rows (sentences) in source | 74,004,228 |
| Documents detected | 6,779 |
| Documents kept | **4,086** |
| Documents dropped (< 8 sentences) | 973 |
| Documents dropped (near-duplicate) | 1,720 |
| Sentences kept | **33,649,142** |

Drop rate: ~40% of detected documents removed (mostly same-book re-uploads
and too-short documents).

## Source & licensing

- **Source dataset:** [`SamuelYang/bookcorpus`](https://huggingface.co/datasets/SamuelYang/bookcorpus)
- **Original corpus:** BookCorpus (Zhu et al., 2015), originally scraped from
  Smashwords. The original BookCorpus has well-documented provenance and
  consent concerns; downstream users should review them before commercial use.
- This cleaned derivative is released under the **MIT License** for the
  cleaning code and structuring effort. The underlying text retains whatever
  rights apply to the upstream source.