dev/repackage_data_reference.py

"""
Repackage a given dataset into simple parquet shards:

- each shard is ~100MB in size (after zstd compression)
- parquets are written with row group size of 1000
- shuffle the dataset

This will be uploaded to HuggingFace for hosting.
The big deal is that our DataLoader will be able to stream
the data and cache it along the way on disk, decreasing the
training latency.

Historical context:
Originally, nanochat used the FinewebEdu-100B dataset.
Then we switched to the ClimbMix-400B dataset due to superior performance.
This script documents how both were prepared.

The outputs are here:

https://huggingface.co/datasets/karpathy/fineweb-edu-100b-shuffle
https://huggingface.co/datasets/karpathy/climbmix-400b-shuffle

NOTE: This file is meant only as reference/documentation of the
dataset preparation and it is not used during the project runtime.
"""
import os
import time

from datasets import load_dataset
import pyarrow.parquet as pq
import pyarrow as pa

# You can change these:
dataset_tag = "climbmix"
upload_to_hf = True

# Dataset configurations:
if dataset_tag == "fineweb_edu":
    dataset_kwargs = {
        "path": "HuggingFaceFW/fineweb-edu",
        "split": "train",
        "name": "sample-100BT", # ~100B GPT-2 tokens at ~3 chars/token => ~300B chars total
    }
    output_dirname = "fineweb_edu"
    data_column_name = "text"
    tokenizer = None
    upload_tag = "fineweb-edu-100b-shuffle"

elif dataset_tag == "climbmix":
    import tiktoken # the ClimbMix data is stored tokenized with GPT-2 tokenizer
    dataset_kwargs = {
        "path": "nvidia/Nemotron-ClimbMix",
        "split": "train",
    }
    output_dirname = "climbmix"
    data_column_name = "tokens"
    tokenizer = tiktoken.encoding_for_model("gpt-2")
    upload_tag = "climbmix-400b-shuffle"

else:
    raise ValueError(f"Unknown dataset tag: {dataset_tag}")

# Source dataset
ds = load_dataset(**dataset_kwargs)

# Shuffle to scramble the order
ds = ds.shuffle(seed=42)
ndocs = len(ds) # total number of documents to process
print(f"Total number of documents: {ndocs}")

# Repackage into parquet files
output_dir = f"/home/ubuntu/.cache/nanochat/base_data_{output_dirname}"
os.makedirs(output_dir, exist_ok=True)

# Write to parquet files
chars_per_shard = 250_000_000
row_group_size = 1024 # HF uses 1000 but we use multiple of 2, nicer for distributed data loader later
shard_docs = []
shard_index = 0
shard_characters = 0
total_docs_processed = 0
total_time_spent = 0
t0 = time.time()
for doc in ds:
    data = doc[data_column_name]
    text = tokenizer.decode(data) if tokenizer is not None else data
    shard_docs.append(text)
    shard_characters += len(text)
    collected_enough_chars = shard_characters >= chars_per_shard
    docs_multiple_of_row_group_size = len(shard_docs) % row_group_size == 0
    if collected_enough_chars and docs_multiple_of_row_group_size: # leads to ~100MB of text (compressed)
        shard_path = os.path.join(output_dir, f"shard_{shard_index:05d}.parquet")
        shard_table = pa.Table.from_pydict({"text": shard_docs})
        pq.write_table(
            shard_table,
            shard_path,
            row_group_size=row_group_size,
            use_dictionary=False, # this is usually used for categorical data
            compression="zstd", # Valid values: {‘NONE’, ‘SNAPPY’, ‘GZIP’, ‘BROTLI’, ‘LZ4’, ‘ZSTD’}
            compression_level=3,
            write_statistics=False, # not needed for text
        )
        t1 = time.time()
        dt = t1 - t0 # for this shard alone
        t0 = t1
        total_docs_processed += len(shard_docs)
        total_time_spent += dt
        remaining_docs = ndocs - total_docs_processed
        avg_time_per_doc = total_time_spent / total_docs_processed
        remaining_time = remaining_docs * avg_time_per_doc
        remaining_time_hours = remaining_time / 3600
        print(f"Wrote {shard_path}. #documents: {len(shard_docs)} | #characters: {shard_characters} | time: {dt:.2f}s | remaining time: {remaining_time_hours:.2f}h")
        shard_docs = []
        shard_characters = 0
        shard_index += 1

# Demonstration of how the data was later uploaded to HuggingFace
if upload_to_hf:
    from huggingface_hub import HfApi
    token = os.getenv("HF_TOKEN")
    api = HfApi(token=token)
    api.upload_large_folder(
        folder_path=output_dir,
        repo_id=f"karpathy/{upload_tag}",
        repo_type="dataset",
    )