Title: Add `batch` method to `Dataset` class
State: closed

This PR introduces a new `batch` method to the `Dataset` class, aligning its functionality with the `IterableDataset.batch()` method (implemented in #7054). The implementation uses as well the existing `map` method for efficient batching of examples.

Key changes:
- Add `batch` method to `Dataset` class in `arrow_dataset.py`
- Utilize `map` method for batching

Closes #7063

Once the approach is approved, i will create the tests and update the documentation.

Comments:
Looks good to me ! :)

you might want to add the `map` num_proc argument as well, for people who want to make it run faster

Thanks for the feedback @lhoestq! The last commits include:
- Adding the `num_proc` parameter to `batch`
- Adding tests similar to the one done for `IterableDataset.batch()`
- Updated the documentation -> I think they are actually misplaced in the `Stream` page. But could not find a better place atm. Where would you put this documentation?

WDYT?

You can put the documentation in process.mdx :)

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_7064). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

I reset the head to the commit before I added the `Dataset.batch()` documentation to `stream.mdx` and instead added the documentation to `process.mdx`. 

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005736 / 0.011353 (-0.005617) | 0.003959 / 0.011008 (-0.007049) | 0.063259 / 0.038508 (0.024751) | 0.030705 / 0.023109 (0.007596) | 0.245706 / 0.275898 (-0.030192) | 0.278766 / 0.323480 (-0.044714) | 0.003354 / 0.007986 (-0.004632) | 0.004246 / 0.004328 (-0.000082) | 0.049346 / 0.004250 (0.045095) | 0.046439 / 0.037052 (0.009386) | 0.257930 / 0.258489 (-0.000559) | 0.295562 / 0.293841 (0.001722) | 0.030529 / 0.128546 (-0.098017) | 0.012465 / 0.075646 (-0.063182) | 0.205595 / 0.419271 (-0.213677) | 0.036319 / 0.043533 (-0.007214) | 0.243872 / 0.255139 (-0.011267) | 0.275834 / 0.283200 (-0.007366) | 0.020330 / 0.141683 (-0.121353) | 1.108337 / 1.452155 (-0.343817) | 1.150406 / 1.492716 (-0.342310) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.113498 / 0.018006 (0.095491) | 0.306654 / 0.000490 (0.306164) | 0.000238 / 0.000200 (0.000038) | 0.000043 / 0.000054 (-0.000012) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.019092 / 0.037411 (-0.018319) | 0.063180 / 0.014526 (0.048654) | 0.078244 / 0.176557 (-0.098313) | 0.126106 / 0.737135 (-0.611030) | 0.078651 / 0.296338 (-0.217687) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.284132 / 0.215209 (0.068923) | 2.781250 / 2.077655 (0.703595) | 1.471864 / 1.504120 (-0.032256) | 1.354661 / 1.541195 (-0.186534) | 1.362839 / 1.468490 (-0.105651) | 0.719126 / 4.584777 (-3.865651) | 2.396969 / 3.745712 (-1.348743) | 2.987924 / 5.269862 (-2.281938) | 1.910555 / 4.565676 (-2.655121) | 0.078612 / 0.424275 (-0.345663) | 0.005170 / 0.007607 (-0.002437) | 0.333876 / 0.226044 (0.107832) | 3.298340 / 2.268929 (1.029412) | 1.853332 / 55.444624 (-53.591292) | 1.551919 / 6.876477 (-5.324557) | 1.585677 / 2.142072 (-0.556395) | 0.802487 / 4.805227 (-4.002741) | 0.134828 / 6.500664 (-6.365837) | 0.041966 / 0.075469 (-0.033503) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.992277 / 1.841788 (-0.849511) | 11.626887 / 8.074308 (3.552578) | 9.715623 / 10.191392 (-0.475769) | 0.140306 / 0.680424 (-0.540117) | 0.014528 / 0.534201 (-0.519673) | 0.306247 / 0.579283 (-0.273036) | 0.263067 / 0.434364 (-0.171297) | 0.342325 / 0.540337 (-0.198013) | 0.432299 / 1.386936 (-0.954637) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.006004 / 0.011353 (-0.005349) | 0.003890 / 0.011008 (-0.007118) | 0.050408 / 0.038508 (0.011900) | 0.031880 / 0.023109 (0.008771) | 0.273114 / 0.275898 (-0.002784) | 0.296653 / 0.323480 (-0.026826) | 0.004569 / 0.007986 (-0.003416) | 0.002831 / 0.004328 (-0.001497) | 0.050032 / 0.004250 (0.045782) | 0.040468 / 0.037052 (0.003415) | 0.284718 / 0.258489 (0.026229) | 0.321754 / 0.293841 (0.027913) | 0.033863 / 0.128546 (-0.094684) | 0.012183 / 0.075646 (-0.063463) | 0.060805 / 0.419271 (-0.358466) | 0.034919 / 0.043533 (-0.008614) | 0.274354 / 0.255139 (0.019215) | 0.293477 / 0.283200 (0.010277) | 0.019418 / 0.141683 (-0.122265) | 1.151571 / 1.452155 (-0.300584) | 1.217174 / 1.492716 (-0.275542) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.097326 / 0.018006 (0.079320) | 0.316277 / 0.000490 (0.315787) | 0.000225 / 0.000200 (0.000025) | 0.000045 / 0.000054 (-0.000009) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.022932 / 0.037411 (-0.014479) | 0.077455 / 0.014526 (0.062929) | 0.088949 / 0.176557 (-0.087608) | 0.129447 / 0.737135 (-0.607688) | 0.093705 / 0.296338 (-0.202634) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.303918 / 0.215209 (0.088709) | 2.973866 / 2.077655 (0.896211) | 1.593165 / 1.504120 (0.089045) | 1.465312 / 1.541195 (-0.075883) | 1.484503 / 1.468490 (0.016013) | 0.731849 / 4.584777 (-3.852928) | 0.953337 / 3.745712 (-2.792375) | 2.887815 / 5.269862 (-2.382047) | 1.923618 / 4.565676 (-2.642058) | 0.080073 / 0.424275 (-0.344202) | 0.005460 / 0.007607 (-0.002148) | 0.359876 / 0.226044 (0.133832) | 3.532251 / 2.268929 (1.263323) | 1.987778 / 55.444624 (-53.456846) | 1.685572 / 6.876477 (-5.190905) | 1.827141 / 2.142072 (-0.314932) | 0.815953 / 4.805227 (-3.989274) | 0.136698 / 6.500664 (-6.363967) | 0.042185 / 0.075469 (-0.033285) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.032508 / 1.841788 (-0.809280) | 12.526918 / 8.074308 (4.452610) | 10.202942 / 10.191392 (0.011550) | 0.145920 / 0.680424 (-0.534504) | 0.015643 / 0.534201 (-0.518558) | 0.300465 / 0.579283 (-0.278818) | 0.126786 / 0.434364 (-0.307578) | 0.342885 / 0.540337 (-0.197453) | 0.438139 / 1.386936 (-0.948797) |

</details>
</details>

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