Fix cast from fixed size list to variable size list

Fix #6242 

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<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) | 0.006784 / 0.011353 (-0.004569) | 0.004051 / 0.011008 (-0.006957) | 0.083790 / 0.038508 (0.045282) | 0.081219 / 0.023109 (0.058110) | 0.313195 / 0.275898 (0.037297) | 0.336954 / 0.323480 (0.013475) | 0.004324 / 0.007986 (-0.003662) | 0.004516 / 0.004328 (0.000188) | 0.065051 / 0.004250 (0.060801) | 0.057647 / 0.037052 (0.020595) | 0.316675 / 0.258489 (0.058186) | 0.357936 / 0.293841 (0.064095) | 0.030980 / 0.128546 (-0.097566) | 0.008844 / 0.075646 (-0.066802) | 0.287027 / 0.419271 (-0.132245) | 0.052130 / 0.043533 (0.008597) | 0.308125 / 0.255139 (0.052986) | 0.337345 / 0.283200 (0.054145) | 0.025781 / 0.141683 (-0.115902) | 1.466161 / 1.452155 (0.014006) | 1.565824 / 1.492716 (0.073108) |

### 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) | 0.299112 / 0.018006 (0.281106) | 0.640520 / 0.000490 (0.640030) | 0.008846 / 0.000200 (0.008647) | 0.000273 / 0.000054 (0.000219) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.029853 / 0.037411 (-0.007559) | 0.081697 / 0.014526 (0.067172) | 0.099110 / 0.176557 (-0.077447) | 0.155864 / 0.737135 (-0.581271) | 0.098749 / 0.296338 (-0.197590) |

### 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) | 0.385722 / 0.215209 (0.170512) | 3.851490 / 2.077655 (1.773835) | 1.851995 / 1.504120 (0.347875) | 1.660398 / 1.541195 (0.119204) | 1.769370 / 1.468490 (0.300879) | 0.481523 / 4.584777 (-4.103254) | 3.550449 / 3.745712 (-0.195263) | 3.424782 / 5.269862 (-1.845079) | 2.106470 / 4.565676 (-2.459206) | 0.056500 / 0.424275 (-0.367775) | 0.007891 / 0.007607 (0.000284) | 0.465564 / 0.226044 (0.239520) | 4.662892 / 2.268929 (2.393964) | 2.305424 / 55.444624 (-53.139201) | 1.980524 / 6.876477 (-4.895953) | 2.218423 / 2.142072 (0.076350) | 0.584662 / 4.805227 (-4.220565) | 0.132325 / 6.500664 (-6.368340) | 0.060773 / 0.075469 (-0.014696) |

### 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) | 1.254261 / 1.841788 (-0.587527) | 19.479805 / 8.074308 (11.405497) | 14.222687 / 10.191392 (4.031295) | 0.149829 / 0.680424 (-0.530595) | 0.018630 / 0.534201 (-0.515571) | 0.395284 / 0.579283 (-0.183999) | 0.413385 / 0.434364 (-0.020978) | 0.462931 / 0.540337 (-0.077406) | 0.645359 / 1.386936 (-0.741577) |

</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) | 0.006991 / 0.011353 (-0.004362) | 0.004306 / 0.011008 (-0.006702) | 0.065213 / 0.038508 (0.026705) | 0.082442 / 0.023109 (0.059332) | 0.411294 / 0.275898 (0.135396) | 0.452176 / 0.323480 (0.128696) | 0.005802 / 0.007986 (-0.002183) | 0.003556 / 0.004328 (-0.000772) | 0.066163 / 0.004250 (0.061913) | 0.060680 / 0.037052 (0.023628) | 0.416975 / 0.258489 (0.158486) | 0.456353 / 0.293841 (0.162512) | 0.033584 / 0.128546 (-0.094963) | 0.008687 / 0.075646 (-0.066959) | 0.071300 / 0.419271 (-0.347972) | 0.049382 / 0.043533 (0.005849) | 0.409329 / 0.255139 (0.154190) | 0.434829 / 0.283200 (0.151629) | 0.022966 / 0.141683 (-0.118716) | 1.493847 / 1.452155 (0.041692) | 1.582372 / 1.492716 (0.089656) |

### 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) | 0.280578 / 0.018006 (0.262572) | 0.538122 / 0.000490 (0.537632) | 0.004515 / 0.000200 (0.004315) | 0.000098 / 0.000054 (0.000043) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.033383 / 0.037411 (-0.004028) | 0.093426 / 0.014526 (0.078901) | 0.109314 / 0.176557 (-0.067242) | 0.162349 / 0.737135 (-0.574786) | 0.109849 / 0.296338 (-0.186490) |

### 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) | 0.431073 / 0.215209 (0.215864) | 4.311942 / 2.077655 (2.234287) | 2.291170 / 1.504120 (0.787051) | 2.132266 / 1.541195 (0.591072) | 2.236526 / 1.468490 (0.768036) | 0.492001 / 4.584777 (-4.092776) | 3.523013 / 3.745712 (-0.222699) | 3.413481 / 5.269862 (-1.856381) | 2.112979 / 4.565676 (-2.452698) | 0.058654 / 0.424275 (-0.365621) | 0.007729 / 0.007607 (0.000121) | 0.512027 / 0.226044 (0.285982) | 5.125264 / 2.268929 (2.856336) | 2.836281 / 55.444624 (-52.608344) | 2.447253 / 6.876477 (-4.429224) | 2.711908 / 2.142072 (0.569835) | 0.592598 / 4.805227 (-4.212629) | 0.134837 / 6.500664 (-6.365827) | 0.059813 / 0.075469 (-0.015656) |

### 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) | 1.373464 / 1.841788 (-0.468323) | 20.548983 / 8.074308 (12.474675) | 14.799833 / 10.191392 (4.608441) | 0.168601 / 0.680424 (-0.511823) | 0.020358 / 0.534201 (-0.513843) | 0.398790 / 0.579283 (-0.180494) | 0.416921 / 0.434364 (-0.017443) | 0.480542 / 0.540337 (-0.059795) | 0.645062 / 1.386936 (-0.741874) |

</details>
</details>

![](https://cml.dev/watermark.png#afd6fc193a91cb0461c8bf3b64db6943c23de846 "CML watermark")


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

<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) | 0.008616 / 0.011353 (-0.002737) | 0.004957 / 0.011008 (-0.006051) | 0.102629 / 0.038508 (0.064121) | 0.080492 / 0.023109 (0.057383) | 0.461817 / 0.275898 (0.185919) | 0.487964 / 0.323480 (0.164484) | 0.006336 / 0.007986 (-0.001649) | 0.004607 / 0.004328 (0.000278) | 0.074311 / 0.004250 (0.070061) | 0.060368 / 0.037052 (0.023315) | 0.458076 / 0.258489 (0.199587) | 0.493028 / 0.293841 (0.199187) | 0.044153 / 0.128546 (-0.084394) | 0.014066 / 0.075646 (-0.061581) | 0.369848 / 0.419271 (-0.049424) | 0.061690 / 0.043533 (0.018157) | 0.439728 / 0.255139 (0.184590) | 0.484706 / 0.283200 (0.201506) | 0.034657 / 0.141683 (-0.107026) | 1.710591 / 1.452155 (0.258437) | 1.900225 / 1.492716 (0.407509) |

### 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) | 0.308837 / 0.018006 (0.290831) | 0.579561 / 0.000490 (0.579072) | 0.010163 / 0.000200 (0.009963) | 0.000613 / 0.000054 (0.000558) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.028108 / 0.037411 (-0.009303) | 0.085072 / 0.014526 (0.070546) | 0.103375 / 0.176557 (-0.073182) | 0.173765 / 0.737135 (-0.563371) | 0.102460 / 0.296338 (-0.193879) |

### 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) | 0.602642 / 0.215209 (0.387433) | 5.582537 / 2.077655 (3.504882) | 2.405553 / 1.504120 (0.901434) | 2.057298 / 1.541195 (0.516103) | 2.223787 / 1.468490 (0.755297) | 0.846138 / 4.584777 (-3.738638) | 5.290306 / 3.745712 (1.544594) | 4.836066 / 5.269862 (-0.433795) | 2.951901 / 4.565676 (-1.613775) | 0.099432 / 0.424275 (-0.324843) | 0.009198 / 0.007607 (0.001591) | 0.731370 / 0.226044 (0.505325) | 6.663026 / 2.268929 (4.394098) | 3.200932 / 55.444624 (-52.243692) | 2.486654 / 6.876477 (-4.389823) | 2.833195 / 2.142072 (0.691123) | 0.989481 / 4.805227 (-3.815746) | 0.205176 / 6.500664 (-6.295488) | 0.073760 / 0.075469 (-0.001709) |

### 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) | 1.745494 / 1.841788 (-0.096294) | 24.649294 / 8.074308 (16.574986) | 22.312182 / 10.191392 (12.120790) | 0.245207 / 0.680424 (-0.435217) | 0.031971 / 0.534201 (-0.502230) | 0.495179 / 0.579283 (-0.084104) | 0.603233 / 0.434364 (0.168869) | 0.560906 / 0.540337 (0.020569) | 0.788292 / 1.386936 (-0.598644) |

</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) | 0.008922 / 0.011353 (-0.002431) | 0.005203 / 0.011008 (-0.005805) | 0.074414 / 0.038508 (0.035906) | 0.077552 / 0.023109 (0.054443) | 0.547217 / 0.275898 (0.271319) | 0.625298 / 0.323480 (0.301818) | 0.006135 / 0.007986 (-0.001851) | 0.004163 / 0.004328 (-0.000165) | 0.078014 / 0.004250 (0.073764) | 0.064484 / 0.037052 (0.027431) | 0.562356 / 0.258489 (0.303867) | 0.643613 / 0.293841 (0.349772) | 0.050155 / 0.128546 (-0.078391) | 0.013665 / 0.075646 (-0.061981) | 0.090224 / 0.419271 (-0.329048) | 0.063852 / 0.043533 (0.020319) | 0.560914 / 0.255139 (0.305775) | 0.591531 / 0.283200 (0.308331) | 0.036491 / 0.141683 (-0.105192) | 1.670898 / 1.452155 (0.218743) | 1.783924 / 1.492716 (0.291208) |

### 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) | 0.312764 / 0.018006 (0.294758) | 0.611116 / 0.000490 (0.610626) | 0.006367 / 0.000200 (0.006167) | 0.000130 / 0.000054 (0.000075) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.033967 / 0.037411 (-0.003445) | 0.101550 / 0.014526 (0.087025) | 0.116953 / 0.176557 (-0.059604) | 0.180061 / 0.737135 (-0.557075) | 0.115220 / 0.296338 (-0.181118) |

### 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) | 0.642110 / 0.215209 (0.426901) | 6.361381 / 2.077655 (4.283727) | 2.948175 / 1.504120 (1.444055) | 2.633935 / 1.541195 (1.092740) | 2.822150 / 1.468490 (1.353660) | 0.931412 / 4.584777 (-3.653365) | 5.428540 / 3.745712 (1.682828) | 4.672920 / 5.269862 (-0.596941) | 3.102046 / 4.565676 (-1.463630) | 0.100825 / 0.424275 (-0.323450) | 0.009464 / 0.007607 (0.001857) | 0.774102 / 0.226044 (0.548058) | 7.715003 / 2.268929 (5.446074) | 3.987807 / 55.444624 (-51.456817) | 3.089129 / 6.876477 (-3.787347) | 3.333247 / 2.142072 (1.191174) | 1.012427 / 4.805227 (-3.792800) | 0.200662 / 6.500664 (-6.300002) | 0.072422 / 0.075469 (-0.003047) |

### 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) | 1.680364 / 1.841788 (-0.161424) | 24.484576 / 8.074308 (16.410268) | 21.920990 / 10.191392 (11.729598) | 0.218604 / 0.680424 (-0.461820) | 0.035818 / 0.534201 (-0.498383) | 0.470648 / 0.579283 (-0.108635) | 0.585108 / 0.434364 (0.150744) | 0.539152 / 0.540337 (-0.001185) | 0.763999 / 1.386936 (-0.622937) |

</details>
</details>

![](https://cml.dev/watermark.png#cfed1d09ed6c680085624d96eb99bfb2b0b27599 "CML watermark")


<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) | 0.006304 / 0.011353 (-0.005049) | 0.003884 / 0.011008 (-0.007125) | 0.084847 / 0.038508 (0.046339) | 0.069372 / 0.023109 (0.046263) | 0.318876 / 0.275898 (0.042978) | 0.344733 / 0.323480 (0.021253) | 0.005139 / 0.007986 (-0.002847) | 0.003203 / 0.004328 (-0.001125) | 0.065758 / 0.004250 (0.061507) | 0.054189 / 0.037052 (0.017137) | 0.317475 / 0.258489 (0.058986) | 0.359310 / 0.293841 (0.065469) | 0.030639 / 0.128546 (-0.097908) | 0.008657 / 0.075646 (-0.066989) | 0.289127 / 0.419271 (-0.130144) | 0.052344 / 0.043533 (0.008811) | 0.316122 / 0.255139 (0.060983) | 0.338339 / 0.283200 (0.055140) | 0.022677 / 0.141683 (-0.119006) | 1.551629 / 1.452155 (0.099474) | 1.617917 / 1.492716 (0.125201) |

### 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) | 0.231067 / 0.018006 (0.213061) | 0.450559 / 0.000490 (0.450070) | 0.008484 / 0.000200 (0.008284) | 0.000234 / 0.000054 (0.000179) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.027054 / 0.037411 (-0.010357) | 0.081560 / 0.014526 (0.067034) | 0.094162 / 0.176557 (-0.082395) | 0.148583 / 0.737135 (-0.588552) | 0.093596 / 0.296338 (-0.202742) |

### 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) | 0.388616 / 0.215209 (0.173407) | 3.874905 / 2.077655 (1.797251) | 1.915845 / 1.504120 (0.411725) | 1.746410 / 1.541195 (0.205215) | 1.828789 / 1.468490 (0.360299) | 0.483270 / 4.584777 (-4.101506) | 3.489157 / 3.745712 (-0.256555) | 3.190086 / 5.269862 (-2.079776) | 1.978023 / 4.565676 (-2.587653) | 0.056290 / 0.424275 (-0.367985) | 0.007585 / 0.007607 (-0.000022) | 0.467051 / 0.226044 (0.241007) | 4.665971 / 2.268929 (2.397043) | 2.418550 / 55.444624 (-53.026075) | 2.048338 / 6.876477 (-4.828139) | 2.225275 / 2.142072 (0.083203) | 0.576601 / 4.805227 (-4.228626) | 0.131960 / 6.500664 (-6.368704) | 0.060177 / 0.075469 (-0.015292) |

### 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) | 1.249797 / 1.841788 (-0.591991) | 18.552939 / 8.074308 (10.478631) | 14.016616 / 10.191392 (3.825224) | 0.162869 / 0.680424 (-0.517555) | 0.018105 / 0.534201 (-0.516096) | 0.394838 / 0.579283 (-0.184445) | 0.403378 / 0.434364 (-0.030986) | 0.460931 / 0.540337 (-0.079407) | 0.637365 / 1.386936 (-0.749571) |

</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) | 0.006497 / 0.011353 (-0.004856) | 0.003928 / 0.011008 (-0.007080) | 0.063958 / 0.038508 (0.025450) | 0.069609 / 0.023109 (0.046500) | 0.401599 / 0.275898 (0.125701) | 0.428128 / 0.323480 (0.104648) | 0.005296 / 0.007986 (-0.002689) | 0.003332 / 0.004328 (-0.000996) | 0.063903 / 0.004250 (0.059652) | 0.056303 / 0.037052 (0.019250) | 0.400704 / 0.258489 (0.142214) | 0.435982 / 0.293841 (0.142141) | 0.032434 / 0.128546 (-0.096112) | 0.008570 / 0.075646 (-0.067077) | 0.070788 / 0.419271 (-0.348483) | 0.048252 / 0.043533 (0.004719) | 0.403269 / 0.255139 (0.148130) | 0.419796 / 0.283200 (0.136596) | 0.022598 / 0.141683 (-0.119085) | 1.481627 / 1.452155 (0.029472) | 1.578388 / 1.492716 (0.085672) |

### 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) | 0.224552 / 0.018006 (0.206546) | 0.444059 / 0.000490 (0.443570) | 0.003757 / 0.000200 (0.003557) | 0.000225 / 0.000054 (0.000171) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.032173 / 0.037411 (-0.005239) | 0.092562 / 0.014526 (0.078036) | 0.104972 / 0.176557 (-0.071584) | 0.156467 / 0.737135 (-0.580669) | 0.104274 / 0.296338 (-0.192065) |

### 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) | 0.441693 / 0.215209 (0.226484) | 4.400217 / 2.077655 (2.322562) | 2.393862 / 1.504120 (0.889742) | 2.281178 / 1.541195 (0.739983) | 2.339895 / 1.468490 (0.871405) | 0.488734 / 4.584777 (-4.096043) | 3.523352 / 3.745712 (-0.222360) | 3.216761 / 5.269862 (-2.053101) | 2.007553 / 4.565676 (-2.558123) | 0.058050 / 0.424275 (-0.366225) | 0.007566 / 0.007607 (-0.000041) | 0.515439 / 0.226044 (0.289394) | 5.155086 / 2.268929 (2.886157) | 2.864958 / 55.444624 (-52.579666) | 2.592460 / 6.876477 (-4.284016) | 2.800449 / 2.142072 (0.658376) | 0.588441 / 4.805227 (-4.216786) | 0.131589 / 6.500664 (-6.369075) | 0.059075 / 0.075469 (-0.016394) |

### 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) | 1.353889 / 1.841788 (-0.487898) | 18.938285 / 8.074308 (10.863977) | 14.937141 / 10.191392 (4.745749) | 0.168811 / 0.680424 (-0.511613) | 0.020118 / 0.534201 (-0.514083) | 0.394791 / 0.579283 (-0.184492) | 0.414434 / 0.434364 (-0.019930) | 0.466821 / 0.540337 (-0.073517) | 0.629894 / 1.386936 (-0.757042) |

</details>
</details>

![](https://cml.dev/watermark.png#23921b08390db7dbb3186a8de40dc49a4066da76 "CML watermark")


CI failures are unrelated

<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) | 0.005959 / 0.011353 (-0.005394) | 0.004164 / 0.011008 (-0.006844) | 0.082336 / 0.038508 (0.043828) | 0.070344 / 0.023109 (0.047234) | 0.348032 / 0.275898 (0.072134) | 0.366328 / 0.323480 (0.042848) | 0.003882 / 0.007986 (-0.004104) | 0.003619 / 0.004328 (-0.000709) | 0.063343 / 0.004250 (0.059093) | 0.056617 / 0.037052 (0.019564) | 0.351625 / 0.258489 (0.093136) | 0.395839 / 0.293841 (0.101998) | 0.030842 / 0.128546 (-0.097704) | 0.008363 / 0.075646 (-0.067284) | 0.300535 / 0.419271 (-0.118737) | 0.053303 / 0.043533 (0.009770) | 0.354782 / 0.255139 (0.099643) | 0.364918 / 0.283200 (0.081719) | 0.025365 / 0.141683 (-0.116318) | 1.555009 / 1.452155 (0.102854) | 1.597443 / 1.492716 (0.104727) |

### 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) | 0.239808 / 0.018006 (0.221801) | 0.488164 / 0.000490 (0.487675) | 0.013183 / 0.000200 (0.012983) | 0.000483 / 0.000054 (0.000429) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.027938 / 0.037411 (-0.009473) | 0.078521 / 0.014526 (0.063995) | 0.095498 / 0.176557 (-0.081059) | 0.150884 / 0.737135 (-0.586251) | 0.097577 / 0.296338 (-0.198762) |

### 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) | 0.384546 / 0.215209 (0.169337) | 4.037707 / 2.077655 (1.960053) | 1.940321 / 1.504120 (0.436201) | 1.716741 / 1.541195 (0.175546) | 1.837200 / 1.468490 (0.368710) | 0.502112 / 4.584777 (-4.082665) | 3.770452 / 3.745712 (0.024740) | 3.325691 / 5.269862 (-1.944171) | 2.015622 / 4.565676 (-2.550055) | 0.056246 / 0.424275 (-0.368029) | 0.007320 / 0.007607 (-0.000287) | 0.445553 / 0.226044 (0.219509) | 4.567233 / 2.268929 (2.298304) | 2.319531 / 55.444624 (-53.125093) | 1.968664 / 6.876477 (-4.907813) | 2.122349 / 2.142072 (-0.019724) | 0.573688 / 4.805227 (-4.231540) | 0.131410 / 6.500664 (-6.369254) | 0.062767 / 0.075469 (-0.012702) |

### 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) | 1.255244 / 1.841788 (-0.586543) | 19.042480 / 8.074308 (10.968172) | 13.935342 / 10.191392 (3.743950) | 0.161259 / 0.680424 (-0.519165) | 0.020582 / 0.534201 (-0.513619) | 0.391365 / 0.579283 (-0.187918) | 0.417462 / 0.434364 (-0.016902) | 0.473121 / 0.540337 (-0.067216) | 0.674768 / 1.386936 (-0.712168) |

</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) | 0.006299 / 0.011353 (-0.005054) | 0.003969 / 0.011008 (-0.007040) | 0.063558 / 0.038508 (0.025050) | 0.073847 / 0.023109 (0.050738) | 0.407064 / 0.275898 (0.131166) | 0.440695 / 0.323480 (0.117215) | 0.005783 / 0.007986 (-0.002203) | 0.003517 / 0.004328 (-0.000812) | 0.065721 / 0.004250 (0.061470) | 0.056390 / 0.037052 (0.019338) | 0.419019 / 0.258489 (0.160530) | 0.450721 / 0.293841 (0.156880) | 0.034094 / 0.128546 (-0.094452) | 0.008594 / 0.075646 (-0.067052) | 0.069254 / 0.419271 (-0.350017) | 0.049218 / 0.043533 (0.005685) | 0.413312 / 0.255139 (0.158173) | 0.439454 / 0.283200 (0.156255) | 0.021481 / 0.141683 (-0.120202) | 1.517536 / 1.452155 (0.065382) | 1.530532 / 1.492716 (0.037815) |

### 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) | 0.235392 / 0.018006 (0.217386) | 0.477371 / 0.000490 (0.476881) | 0.007070 / 0.000200 (0.006870) | 0.000132 / 0.000054 (0.000077) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.031909 / 0.037411 (-0.005502) | 0.092459 / 0.014526 (0.077933) | 0.105795 / 0.176557 (-0.070761) | 0.157745 / 0.737135 (-0.579390) | 0.104187 / 0.296338 (-0.192152) |

### 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) | 0.424385 / 0.215209 (0.209176) | 4.445371 / 2.077655 (2.367716) | 2.423639 / 1.504120 (0.919519) | 2.188167 / 1.541195 (0.646972) | 2.171023 / 1.468490 (0.702532) | 0.483566 / 4.584777 (-4.101211) | 3.825702 / 3.745712 (0.079990) | 3.276350 / 5.269862 (-1.993512) | 2.063075 / 4.565676 (-2.502602) | 0.061628 / 0.424275 (-0.362647) | 0.008176 / 0.007607 (0.000569) | 0.506697 / 0.226044 (0.280653) | 5.067924 / 2.268929 (2.798995) | 2.785567 / 55.444624 (-52.659057) | 2.457340 / 6.876477 (-4.419137) | 2.599646 / 2.142072 (0.457574) | 0.581550 / 4.805227 (-4.223677) | 0.131712 / 6.500664 (-6.368952) | 0.058776 / 0.075469 (-0.016693) |

### 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) | 1.356639 / 1.841788 (-0.485148) | 20.103463 / 8.074308 (12.029155) | 14.481010 / 10.191392 (4.289618) | 0.162870 / 0.680424 (-0.517554) | 0.023197 / 0.534201 (-0.511004) | 0.413042 / 0.579283 (-0.166241) | 0.427494 / 0.434364 (-0.006870) | 0.508457 / 0.540337 (-0.031880) | 0.662412 / 1.386936 (-0.724524) |

</details>
</details>

![](https://cml.dev/watermark.png#05fe5c06d42f84408b933c2809acb9b7449cbbb3 "CML watermark")