Title: Fix RuntimeError: Sharding is ambiguous for this dataset
State: closed

This PR fixes the RuntimeError: Sharding is ambiguous for this dataset.

The error for ambiguous sharding will be raised only if num_proc > 1.

Fix #5415, fix #5414.
Fix https://huggingface.co/datasets/ami/discussions/3.

Comments:
_The documentation is not available anymore as the PR was closed or merged._

By the way, do we know how many datasets are impacted by this issue?

Maybe we should do a patch release with this fix.

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

PyArrow==6.0.0

<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) | 0.009256 / 0.011353 (-0.002097) | 0.005033 / 0.011008 (-0.005975) | 0.099346 / 0.038508 (0.060838) | 0.035204 / 0.023109 (0.012095) | 0.303017 / 0.275898 (0.027119) | 0.335632 / 0.323480 (0.012152) | 0.007953 / 0.007986 (-0.000033) | 0.005806 / 0.004328 (0.001477) | 0.076121 / 0.004250 (0.071871) | 0.041164 / 0.037052 (0.004112) | 0.305536 / 0.258489 (0.047047) | 0.348452 / 0.293841 (0.054611) | 0.037704 / 0.128546 (-0.090842) | 0.011982 / 0.075646 (-0.063664) | 0.333264 / 0.419271 (-0.086008) | 0.047738 / 0.043533 (0.004205) | 0.310126 / 0.255139 (0.054987) | 0.318719 / 0.283200 (0.035519) | 0.098933 / 0.141683 (-0.042750) | 1.421058 / 1.452155 (-0.031096) | 1.554771 / 1.492716 (0.062054) |

### 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) | 0.258627 / 0.018006 (0.240620) | 0.450814 / 0.000490 (0.450324) | 0.011288 / 0.000200 (0.011088) | 0.000136 / 0.000054 (0.000081) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.027004 / 0.037411 (-0.010407) | 0.109067 / 0.014526 (0.094541) | 0.120401 / 0.176557 (-0.056155) | 0.158336 / 0.737135 (-0.578799) | 0.126244 / 0.296338 (-0.170094) |

### 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) | 0.401847 / 0.215209 (0.186638) | 4.006003 / 2.077655 (1.928348) | 1.806342 / 1.504120 (0.302223) | 1.619751 / 1.541195 (0.078556) | 1.709660 / 1.468490 (0.241170) | 0.692444 / 4.584777 (-3.892333) | 3.853691 / 3.745712 (0.107979) | 2.143910 / 5.269862 (-3.125951) | 1.471600 / 4.565676 (-3.094076) | 0.084589 / 0.424275 (-0.339686) | 0.012276 / 0.007607 (0.004669) | 0.506529 / 0.226044 (0.280485) | 5.028361 / 2.268929 (2.759432) | 2.277660 / 55.444624 (-53.166964) | 1.930365 / 6.876477 (-4.946112) | 1.965494 / 2.142072 (-0.176579) | 0.826752 / 4.805227 (-3.978475) | 0.165050 / 6.500664 (-6.335614) | 0.062702 / 0.075469 (-0.012767) |

### 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) | 1.234539 / 1.841788 (-0.607249) | 15.067401 / 8.074308 (6.993093) | 14.041920 / 10.191392 (3.850528) | 0.162590 / 0.680424 (-0.517834) | 0.028941 / 0.534201 (-0.505260) | 0.438518 / 0.579283 (-0.140765) | 0.443787 / 0.434364 (0.009423) | 0.516671 / 0.540337 (-0.023666) | 0.609036 / 1.386936 (-0.777900) |

</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) | 0.007535 / 0.011353 (-0.003818) | 0.005283 / 0.011008 (-0.005725) | 0.097116 / 0.038508 (0.058608) | 0.033357 / 0.023109 (0.010247) | 0.383398 / 0.275898 (0.107500) | 0.425516 / 0.323480 (0.102037) | 0.006039 / 0.007986 (-0.001947) | 0.004074 / 0.004328 (-0.000255) | 0.073207 / 0.004250 (0.068956) | 0.052153 / 0.037052 (0.015101) | 0.386385 / 0.258489 (0.127896) | 0.429900 / 0.293841 (0.136059) | 0.038341 / 0.128546 (-0.090205) | 0.012417 / 0.075646 (-0.063230) | 0.333859 / 0.419271 (-0.085413) | 0.051157 / 0.043533 (0.007625) | 0.395022 / 0.255139 (0.139883) | 0.402462 / 0.283200 (0.119262) | 0.105207 / 0.141683 (-0.036475) | 1.510679 / 1.452155 (0.058524) | 1.584205 / 1.492716 (0.091489) |

### 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) | 0.225805 / 0.018006 (0.207799) | 0.452109 / 0.000490 (0.451619) | 0.000429 / 0.000200 (0.000229) | 0.000057 / 0.000054 (0.000002) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.029653 / 0.037411 (-0.007759) | 0.112609 / 0.014526 (0.098083) | 0.121828 / 0.176557 (-0.054728) | 0.159003 / 0.737135 (-0.578133) | 0.129306 / 0.296338 (-0.167033) |

### 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) | 0.453001 / 0.215209 (0.237792) | 4.514882 / 2.077655 (2.437228) | 2.277494 / 1.504120 (0.773374) | 2.073870 / 1.541195 (0.532675) | 2.153346 / 1.468490 (0.684856) | 0.698363 / 4.584777 (-3.886414) | 3.921763 / 3.745712 (0.176051) | 2.123133 / 5.269862 (-3.146729) | 1.347618 / 4.565676 (-3.218058) | 0.085654 / 0.424275 (-0.338621) | 0.012059 / 0.007607 (0.004452) | 0.568183 / 0.226044 (0.342139) | 5.720047 / 2.268929 (3.451119) | 2.777973 / 55.444624 (-52.666651) | 2.453426 / 6.876477 (-4.423051) | 2.523977 / 2.142072 (0.381905) | 0.841979 / 4.805227 (-3.963248) | 0.167958 / 6.500664 (-6.332706) | 0.064929 / 0.075469 (-0.010540) |

### 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) | 1.235297 / 1.841788 (-0.606491) | 15.883598 / 8.074308 (7.809290) | 14.395328 / 10.191392 (4.203936) | 0.162401 / 0.680424 (-0.518022) | 0.017806 / 0.534201 (-0.516394) | 0.423853 / 0.579283 (-0.155430) | 0.423266 / 0.434364 (-0.011098) | 0.490351 / 0.540337 (-0.049986) | 0.588116 / 1.386936 (-0.798820) |

</details>
</details>

![](https://cml.dev/watermark.png#bb3fbfa162bb4700e23d084826b4b7f6d97284be "CML watermark")


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

PyArrow==6.0.0

<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) | 0.010759 / 0.011353 (-0.000594) | 0.005748 / 0.011008 (-0.005260) | 0.119195 / 0.038508 (0.080687) | 0.033476 / 0.023109 (0.010367) | 0.364081 / 0.275898 (0.088183) | 0.422456 / 0.323480 (0.098976) | 0.009780 / 0.007986 (0.001795) | 0.006170 / 0.004328 (0.001841) | 0.093242 / 0.004250 (0.088991) | 0.041049 / 0.037052 (0.003997) | 0.372132 / 0.258489 (0.113643) | 0.442501 / 0.293841 (0.148660) | 0.054889 / 0.128546 (-0.073657) | 0.018302 / 0.075646 (-0.057345) | 0.378899 / 0.419271 (-0.040373) | 0.058455 / 0.043533 (0.014922) | 0.356141 / 0.255139 (0.101002) | 0.400866 / 0.283200 (0.117666) | 0.103384 / 0.141683 (-0.038299) | 1.629867 / 1.452155 (0.177713) | 1.693939 / 1.492716 (0.201222) |

### 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) | 0.240484 / 0.018006 (0.222478) | 0.509137 / 0.000490 (0.508648) | 0.000450 / 0.000200 (0.000250) | 0.000080 / 0.000054 (0.000026) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.025856 / 0.037411 (-0.011555) | 0.113214 / 0.014526 (0.098689) | 0.119420 / 0.176557 (-0.057136) | 0.158663 / 0.737135 (-0.578473) | 0.123542 / 0.296338 (-0.172797) |

### 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) | 0.555900 / 0.215209 (0.340691) | 5.580295 / 2.077655 (3.502640) | 2.216640 / 1.504120 (0.712520) | 1.904944 / 1.541195 (0.363749) | 1.865839 / 1.468490 (0.397349) | 1.158325 / 4.584777 (-3.426452) | 5.097420 / 3.745712 (1.351708) | 2.881775 / 5.269862 (-2.388087) | 2.068896 / 4.565676 (-2.496780) | 0.129028 / 0.424275 (-0.295247) | 0.014075 / 0.007607 (0.006468) | 0.698874 / 0.226044 (0.472830) | 7.131225 / 2.268929 (4.862296) | 2.901686 / 55.444624 (-52.542939) | 2.186146 / 6.876477 (-4.690330) | 2.251172 / 2.142072 (0.109100) | 1.342264 / 4.805227 (-3.462963) | 0.232045 / 6.500664 (-6.268619) | 0.073520 / 0.075469 (-0.001949) |

### 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) | 1.431314 / 1.841788 (-0.410474) | 16.313055 / 8.074308 (8.238747) | 18.451552 / 10.191392 (8.260160) | 0.232875 / 0.680424 (-0.447549) | 0.042170 / 0.534201 (-0.492031) | 0.495261 / 0.579283 (-0.084022) | 0.582901 / 0.434364 (0.148537) | 0.582049 / 0.540337 (0.041712) | 0.681122 / 1.386936 (-0.705814) |

</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) | 0.008131 / 0.011353 (-0.003222) | 0.006162 / 0.011008 (-0.004847) | 0.113721 / 0.038508 (0.075213) | 0.030797 / 0.023109 (0.007688) | 0.413108 / 0.275898 (0.137210) | 0.449968 / 0.323480 (0.126488) | 0.006126 / 0.007986 (-0.001860) | 0.004848 / 0.004328 (0.000519) | 0.085465 / 0.004250 (0.081214) | 0.045817 / 0.037052 (0.008764) | 0.419360 / 0.258489 (0.160871) | 0.489077 / 0.293841 (0.195236) | 0.050841 / 0.128546 (-0.077705) | 0.020646 / 0.075646 (-0.055000) | 0.379838 / 0.419271 (-0.039434) | 0.068897 / 0.043533 (0.025365) | 0.422182 / 0.255139 (0.167043) | 0.435529 / 0.283200 (0.152330) | 0.115299 / 0.141683 (-0.026384) | 1.655134 / 1.452155 (0.202979) | 1.835198 / 1.492716 (0.342481) |

### 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) | 0.207041 / 0.018006 (0.189034) | 0.491263 / 0.000490 (0.490773) | 0.003554 / 0.000200 (0.003354) | 0.000104 / 0.000054 (0.000050) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.030830 / 0.037411 (-0.006582) | 0.127003 / 0.014526 (0.112477) | 0.142901 / 0.176557 (-0.033656) | 0.177570 / 0.737135 (-0.559565) | 0.137758 / 0.296338 (-0.158580) |

### 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) | 0.632820 / 0.215209 (0.417611) | 6.215535 / 2.077655 (4.137880) | 2.615310 / 1.504120 (1.111190) | 2.261431 / 1.541195 (0.720236) | 2.220570 / 1.468490 (0.752080) | 1.215820 / 4.584777 (-3.368957) | 5.247680 / 3.745712 (1.501968) | 3.120054 / 5.269862 (-2.149807) | 1.950947 / 4.565676 (-2.614730) | 0.149980 / 0.424275 (-0.274295) | 0.015241 / 0.007607 (0.007634) | 0.879714 / 0.226044 (0.653670) | 7.941913 / 2.268929 (5.672984) | 3.512456 / 55.444624 (-51.932168) | 2.693833 / 6.876477 (-4.182644) | 2.772780 / 2.142072 (0.630708) | 1.459581 / 4.805227 (-3.345646) | 0.264820 / 6.500664 (-6.235844) | 0.076698 / 0.075469 (0.001228) |

### 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) | 1.437719 / 1.841788 (-0.404068) | 16.750309 / 8.074308 (8.676001) | 18.646776 / 10.191392 (8.455384) | 0.227858 / 0.680424 (-0.452566) | 0.024239 / 0.534201 (-0.509962) | 0.486172 / 0.579283 (-0.093111) | 0.574731 / 0.434364 (0.140367) | 0.557776 / 0.540337 (0.017439) | 0.672921 / 1.386936 (-0.714015) |

</details>
</details>

![](https://cml.dev/watermark.png#bb3fbfa162bb4700e23d084826b4b7f6d97284be "CML watermark")