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Answer:

from datasets import load_dataset
ds = load_dataset("imdb", split="train")

ds = ds.with_format("arrow")
for table in ds.iter(batch_size=1000):   # pyarrow.Table batches
    print(table.num_rows)

import pyarrow.compute as pc
ds = ds.map(lambda t: t.append_column("len", pc.utf8_length(t["text"])), batched=True)

Why Arrow

• Zero-copy reads: almost no serialization overhead.
• Language-agnostic: the same data works from many languages.
• This is possible because the Arrow data is actually memory-mapped from disk, and not loaded in memory. (S2)

Claims

• id: C1 claim: You can set the dataset format to pyarrow with with_format. source: S1 evidence: "you can set the format of the dataset to pyarrow using Dataset.with_format():"
• id: C2 claim: Datasets uses Arrow for its local caching system. source: S2 evidence: "Datasets uses Arrow for its local caching system."
• id: C3 claim: Arrow stores data in a columnar memory layout. source: S2 evidence: "It is a specific data format that stores data in a columnar memory layout."
• id: C4 claim: Arrow's format allows zero-copy reads. source: S2 evidence: "Arrow’s standard format allows zero-copy reads which removes virtually all serialization overhead."
• id: C5 claim: Arrow data is memory-mapped from disk, not loaded in memory. source: S2 evidence: "the Arrow data is actually memory-mapped from disk, and not loaded in memory."

Sources

• [S1] Use with PyArrow · Hugging Face. Hugging Face docs. https://huggingface.co/docs/datasets/use_with_pyarrow . License: Apache-2.0 (huggingface docs repos). Accessed 2026-11-04.
• [S2] Datasets 🤝 Arrow · Hugging Face. Hugging Face docs. https://huggingface.co/docs/datasets/about_arrow . License: Apache-2.0 (huggingface docs repos). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_61ehd4gd,
  author = {{iinventedlight}},
  title = {{Hugging Face Datasets and Apache Arrow}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/hf-datasets-pyarrow/},
  note = {Permanent ID iil:note:61ehd4gd. License: CC-BY-4.0.},
}

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