less script docs

+ mark as legacy in some parts of the docs since we'll not build new features for script datasets

Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6993). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

<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) | 0.005810 / 0.011353 (-0.005543) | 0.003984 / 0.011008 (-0.007024) | 0.064347 / 0.038508 (0.025839) | 0.031943 / 0.023109 (0.008834) | 0.252596 / 0.275898 (-0.023302) | 0.274032 / 0.323480 (-0.049448) | 0.003494 / 0.007986 (-0.004492) | 0.002817 / 0.004328 (-0.001511) | 0.050132 / 0.004250 (0.045881) | 0.048008 / 0.037052 (0.010955) | 0.249037 / 0.258489 (-0.009452) | 0.288526 / 0.293841 (-0.005315) | 0.031038 / 0.128546 (-0.097509) | 0.012542 / 0.075646 (-0.063104) | 0.205682 / 0.419271 (-0.213590) | 0.038022 / 0.043533 (-0.005511) | 0.259001 / 0.255139 (0.003862) | 0.267455 / 0.283200 (-0.015744) | 0.021980 / 0.141683 (-0.119703) | 1.123996 / 1.452155 (-0.328159) | 1.173801 / 1.492716 (-0.318915) |

### 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) | 0.102827 / 0.018006 (0.084821) | 0.317210 / 0.000490 (0.316720) | 0.000222 / 0.000200 (0.000022) | 0.000052 / 0.000054 (-0.000002) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.019483 / 0.037411 (-0.017928) | 0.064098 / 0.014526 (0.049572) | 0.076219 / 0.176557 (-0.100337) | 0.122898 / 0.737135 (-0.614237) | 0.080657 / 0.296338 (-0.215681) |

### 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) | 0.278378 / 0.215209 (0.063169) | 2.792314 / 2.077655 (0.714659) | 1.516439 / 1.504120 (0.012319) | 1.374052 / 1.541195 (-0.167143) | 1.370848 / 1.468490 (-0.097642) | 0.756002 / 4.584777 (-3.828775) | 2.349581 / 3.745712 (-1.396131) | 2.994094 / 5.269862 (-2.275768) | 1.904242 / 4.565676 (-2.661435) | 0.078769 / 0.424275 (-0.345506) | 0.005103 / 0.007607 (-0.002505) | 0.336331 / 0.226044 (0.110287) | 3.329502 / 2.268929 (1.060574) | 1.863545 / 55.444624 (-53.581079) | 1.554690 / 6.876477 (-5.321787) | 1.588448 / 2.142072 (-0.553624) | 0.787322 / 4.805227 (-4.017905) | 0.138345 / 6.500664 (-6.362320) | 0.042228 / 0.075469 (-0.033241) |

### 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) | 0.968607 / 1.841788 (-0.873181) | 11.972076 / 8.074308 (3.897768) | 9.927608 / 10.191392 (-0.263784) | 0.141666 / 0.680424 (-0.538758) | 0.014591 / 0.534201 (-0.519610) | 0.301995 / 0.579283 (-0.277288) | 0.274360 / 0.434364 (-0.160004) | 0.338396 / 0.540337 (-0.201941) | 0.431081 / 1.386936 (-0.955855) |

</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) | 0.006122 / 0.011353 (-0.005231) | 0.004201 / 0.011008 (-0.006807) | 0.050204 / 0.038508 (0.011695) | 0.033222 / 0.023109 (0.010113) | 0.274357 / 0.275898 (-0.001542) | 0.296238 / 0.323480 (-0.027242) | 0.004542 / 0.007986 (-0.003444) | 0.002880 / 0.004328 (-0.001449) | 0.049103 / 0.004250 (0.044852) | 0.042294 / 0.037052 (0.005242) | 0.286459 / 0.258489 (0.027970) | 0.324988 / 0.293841 (0.031147) | 0.032084 / 0.128546 (-0.096462) | 0.012329 / 0.075646 (-0.063318) | 0.060261 / 0.419271 (-0.359010) | 0.034130 / 0.043533 (-0.009403) | 0.271432 / 0.255139 (0.016293) | 0.306251 / 0.283200 (0.023051) | 0.019744 / 0.141683 (-0.121939) | 1.153483 / 1.452155 (-0.298672) | 1.209126 / 1.492716 (-0.283591) |

### 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) | 0.004737 / 0.018006 (-0.013270) | 0.313458 / 0.000490 (0.312968) | 0.000216 / 0.000200 (0.000017) | 0.000053 / 0.000054 (-0.000001) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.022472 / 0.037411 (-0.014939) | 0.076725 / 0.014526 (0.062199) | 0.091356 / 0.176557 (-0.085201) | 0.132427 / 0.737135 (-0.604708) | 0.091072 / 0.296338 (-0.205266) |

### 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) | 0.294414 / 0.215209 (0.079205) | 2.913695 / 2.077655 (0.836040) | 1.567309 / 1.504120 (0.063189) | 1.448664 / 1.541195 (-0.092531) | 1.466386 / 1.468490 (-0.002105) | 0.718605 / 4.584777 (-3.866172) | 0.951963 / 3.745712 (-2.793749) | 2.812565 / 5.269862 (-2.457297) | 1.886483 / 4.565676 (-2.679193) | 0.077912 / 0.424275 (-0.346363) | 0.005371 / 0.007607 (-0.002236) | 0.349528 / 0.226044 (0.123484) | 3.431049 / 2.268929 (1.162121) | 1.920210 / 55.444624 (-53.524414) | 1.637927 / 6.876477 (-5.238549) | 1.767502 / 2.142072 (-0.374570) | 0.808672 / 4.805227 (-3.996555) | 0.134261 / 6.500664 (-6.366403) | 0.041295 / 0.075469 (-0.034174) |

### 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) | 1.023454 / 1.841788 (-0.818334) | 12.433731 / 8.074308 (4.359423) | 10.413191 / 10.191392 (0.221799) | 0.156813 / 0.680424 (-0.523611) | 0.015446 / 0.534201 (-0.518755) | 0.301935 / 0.579283 (-0.277348) | 0.133655 / 0.434364 (-0.300709) | 0.340296 / 0.540337 (-0.200041) | 0.466314 / 1.386936 (-0.920622) |

</details>
</details>

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Hi @lhoestq,

I was confused by `legacy` prefix added to the [image data loading](https://huggingface.co/docs/datasets/main/en/image_dataset#legacy-loading-script) script section. I have a custom image dataset and have looked through the documentation to find something similar but can't find a good alternative What is now the recommend way to create a custom image dataset then? I want the HF format but will not host it on the hub.

Apologies in advance if this is the wrong place to ask such questions...

We stopped making new features for datasets with scripts for obvious security reasons, that's why they are marked as "legacy". What is blocking you from hosting on HF ?

Hi, thanks for the prompt answer :) I am working on proprietary datasets for the company where I am employed. We want to keep the data in-house but would like to investigate the use of the HF ecosystem.

I see ! Note that it's possible to have private repos on HF (+ dataset viewer) and you can even choose the storage region, if it can help