Fix documentation about batch samplers



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<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) | 0.008874 / 0.011353 (-0.002479) | 0.004685 / 0.011008 (-0.006323) | 0.101478 / 0.038508 (0.062970) | 0.031409 / 0.023109 (0.008300) | 0.305429 / 0.275898 (0.029531) | 0.371777 / 0.323480 (0.048297) | 0.007282 / 0.007986 (-0.000704) | 0.005545 / 0.004328 (0.001217) | 0.078583 / 0.004250 (0.074333) | 0.037171 / 0.037052 (0.000118) | 0.320186 / 0.258489 (0.061696) | 0.347881 / 0.293841 (0.054040) | 0.034005 / 0.128546 (-0.094541) | 0.011534 / 0.075646 (-0.064113) | 0.326079 / 0.419271 (-0.093193) | 0.040856 / 0.043533 (-0.002677) | 0.307327 / 0.255139 (0.052188) | 0.323521 / 0.283200 (0.040321) | 0.090407 / 0.141683 (-0.051276) | 1.481994 / 1.452155 (0.029840) | 1.490372 / 1.492716 (-0.002345) |

### 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) | 0.175161 / 0.018006 (0.157155) | 0.447009 / 0.000490 (0.446519) | 0.003570 / 0.000200 (0.003370) | 0.000072 / 0.000054 (0.000017) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.023868 / 0.037411 (-0.013543) | 0.100791 / 0.014526 (0.086265) | 0.108131 / 0.176557 (-0.068425) | 0.147993 / 0.737135 (-0.589142) | 0.111205 / 0.296338 (-0.185133) |

### 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) | 0.425369 / 0.215209 (0.210160) | 4.241694 / 2.077655 (2.164040) | 2.145403 / 1.504120 (0.641283) | 1.913517 / 1.541195 (0.372322) | 1.887307 / 1.468490 (0.418817) | 0.691615 / 4.584777 (-3.893162) | 3.402233 / 3.745712 (-0.343480) | 1.992532 / 5.269862 (-3.277330) | 1.322292 / 4.565676 (-3.243385) | 0.082862 / 0.424275 (-0.341413) | 0.012595 / 0.007607 (0.004988) | 0.528490 / 0.226044 (0.302445) | 5.313338 / 2.268929 (3.044409) | 2.645037 / 55.444624 (-52.799587) | 2.326279 / 6.876477 (-4.550198) | 2.396955 / 2.142072 (0.254883) | 0.819354 / 4.805227 (-3.985873) | 0.150889 / 6.500664 (-6.349775) | 0.066517 / 0.075469 (-0.008952) |

### 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) | 1.233673 / 1.841788 (-0.608114) | 14.563293 / 8.074308 (6.488985) | 14.317989 / 10.191392 (4.126597) | 0.150767 / 0.680424 (-0.529657) | 0.028972 / 0.534201 (-0.505229) | 0.400547 / 0.579283 (-0.178736) | 0.402267 / 0.434364 (-0.032097) | 0.459375 / 0.540337 (-0.080962) | 0.544419 / 1.386936 (-0.842517) |

</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) | 0.006817 / 0.011353 (-0.004536) | 0.004588 / 0.011008 (-0.006421) | 0.099224 / 0.038508 (0.060716) | 0.027730 / 0.023109 (0.004621) | 0.412310 / 0.275898 (0.136412) | 0.445731 / 0.323480 (0.122252) | 0.005197 / 0.007986 (-0.002788) | 0.003601 / 0.004328 (-0.000728) | 0.076200 / 0.004250 (0.071950) | 0.041813 / 0.037052 (0.004761) | 0.415282 / 0.258489 (0.156793) | 0.457182 / 0.293841 (0.163341) | 0.031920 / 0.128546 (-0.096626) | 0.011712 / 0.075646 (-0.063934) | 0.320859 / 0.419271 (-0.098412) | 0.041466 / 0.043533 (-0.002067) | 0.418156 / 0.255139 (0.163017) | 0.435501 / 0.283200 (0.152302) | 0.090727 / 0.141683 (-0.050955) | 1.484014 / 1.452155 (0.031859) | 1.568072 / 1.492716 (0.075356) |

### 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) | 0.263356 / 0.018006 (0.245350) | 0.410768 / 0.000490 (0.410278) | 0.015983 / 0.000200 (0.015783) | 0.000301 / 0.000054 (0.000246) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.024522 / 0.037411 (-0.012889) | 0.103986 / 0.014526 (0.089460) | 0.109253 / 0.176557 (-0.067303) | 0.142308 / 0.737135 (-0.594827) | 0.114037 / 0.296338 (-0.182302) |

### 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) | 0.452617 / 0.215209 (0.237407) | 4.505215 / 2.077655 (2.427560) | 2.185546 / 1.504120 (0.681426) | 1.995540 / 1.541195 (0.454345) | 1.962875 / 1.468490 (0.494385) | 0.690237 / 4.584777 (-3.894540) | 3.448311 / 3.745712 (-0.297401) | 1.901572 / 5.269862 (-3.368289) | 1.170832 / 4.565676 (-3.394844) | 0.082333 / 0.424275 (-0.341942) | 0.012569 / 0.007607 (0.004962) | 0.547822 / 0.226044 (0.321778) | 5.504180 / 2.268929 (3.235251) | 2.693981 / 55.444624 (-52.750644) | 2.320710 / 6.876477 (-4.555767) | 2.270508 / 2.142072 (0.128435) | 0.803145 / 4.805227 (-4.002083) | 0.152168 / 6.500664 (-6.348496) | 0.067408 / 0.075469 (-0.008061) |

### 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) | 1.260689 / 1.841788 (-0.581099) | 14.281112 / 8.074308 (6.206804) | 14.549742 / 10.191392 (4.358350) | 0.129337 / 0.680424 (-0.551087) | 0.017181 / 0.534201 (-0.517020) | 0.380473 / 0.579283 (-0.198810) | 0.387689 / 0.434364 (-0.046675) | 0.446734 / 0.540337 (-0.093603) | 0.532479 / 1.386936 (-0.854457) |

</details>
</details>

![](https://cml.dev/watermark.png#7972a0b5f1ad2c36023a79686f6ef026f4ffa64f "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) | 0.008953 / 0.011353 (-0.002400) | 0.004917 / 0.011008 (-0.006091) | 0.098699 / 0.038508 (0.060191) | 0.034460 / 0.023109 (0.011351) | 0.294604 / 0.275898 (0.018706) | 0.322709 / 0.323480 (-0.000770) | 0.007780 / 0.007986 (-0.000206) | 0.004061 / 0.004328 (-0.000267) | 0.076134 / 0.004250 (0.071883) | 0.043786 / 0.037052 (0.006734) | 0.302155 / 0.258489 (0.043666) | 0.339779 / 0.293841 (0.045938) | 0.038305 / 0.128546 (-0.090241) | 0.012131 / 0.075646 (-0.063515) | 0.332656 / 0.419271 (-0.086615) | 0.048029 / 0.043533 (0.004496) | 0.303859 / 0.255139 (0.048720) | 0.315861 / 0.283200 (0.032662) | 0.100758 / 0.141683 (-0.040925) | 1.468072 / 1.452155 (0.015918) | 1.521325 / 1.492716 (0.028609) |

### 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) | 0.244975 / 0.018006 (0.226969) | 0.524392 / 0.000490 (0.523902) | 0.003720 / 0.000200 (0.003520) | 0.000087 / 0.000054 (0.000032) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.027704 / 0.037411 (-0.009707) | 0.109048 / 0.014526 (0.094522) | 0.118298 / 0.176557 (-0.058259) | 0.158748 / 0.737135 (-0.578388) | 0.125654 / 0.296338 (-0.170684) |

### 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) | 0.406973 / 0.215209 (0.191764) | 4.057502 / 2.077655 (1.979847) | 1.939847 / 1.504120 (0.435727) | 1.746457 / 1.541195 (0.205262) | 1.698866 / 1.468490 (0.230376) | 0.692884 / 4.584777 (-3.891893) | 3.736988 / 3.745712 (-0.008724) | 2.050122 / 5.269862 (-3.219740) | 1.299808 / 4.565676 (-3.265868) | 0.085285 / 0.424275 (-0.338990) | 0.012768 / 0.007607 (0.005161) | 0.510814 / 0.226044 (0.284770) | 5.105319 / 2.268929 (2.836391) | 2.304003 / 55.444624 (-53.140621) | 1.951123 / 6.876477 (-4.925354) | 1.998504 / 2.142072 (-0.143568) | 0.840235 / 4.805227 (-3.964993) | 0.164521 / 6.500664 (-6.336143) | 0.064215 / 0.075469 (-0.011254) |

### 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) | 1.272520 / 1.841788 (-0.569268) | 14.648110 / 8.074308 (6.573802) | 14.573754 / 10.191392 (4.382362) | 0.170053 / 0.680424 (-0.510371) | 0.029389 / 0.534201 (-0.504811) | 0.438924 / 0.579283 (-0.140359) | 0.433572 / 0.434364 (-0.000792) | 0.517702 / 0.540337 (-0.022635) | 0.600389 / 1.386936 (-0.786547) |

</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) | 0.007362 / 0.011353 (-0.003991) | 0.005451 / 0.011008 (-0.005557) | 0.099336 / 0.038508 (0.060828) | 0.033284 / 0.023109 (0.010174) | 0.377143 / 0.275898 (0.101245) | 0.423724 / 0.323480 (0.100244) | 0.006194 / 0.007986 (-0.001792) | 0.004208 / 0.004328 (-0.000121) | 0.074473 / 0.004250 (0.070223) | 0.049874 / 0.037052 (0.012821) | 0.376012 / 0.258489 (0.117523) | 0.439942 / 0.293841 (0.146101) | 0.037860 / 0.128546 (-0.090686) | 0.012546 / 0.075646 (-0.063100) | 0.349123 / 0.419271 (-0.070148) | 0.048980 / 0.043533 (0.005447) | 0.391205 / 0.255139 (0.136066) | 0.396474 / 0.283200 (0.113274) | 0.105846 / 0.141683 (-0.035836) | 1.502475 / 1.452155 (0.050321) | 1.612303 / 1.492716 (0.119587) |

### 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) | 0.300815 / 0.018006 (0.282809) | 0.542171 / 0.000490 (0.541681) | 0.005465 / 0.000200 (0.005265) | 0.000094 / 0.000054 (0.000039) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.028904 / 0.037411 (-0.008508) | 0.110352 / 0.014526 (0.095827) | 0.123275 / 0.176557 (-0.053282) | 0.161958 / 0.737135 (-0.575178) | 0.133595 / 0.296338 (-0.162743) |

### 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) | 0.438724 / 0.215209 (0.223515) | 4.373633 / 2.077655 (2.295979) | 2.178981 / 1.504120 (0.674861) | 1.992442 / 1.541195 (0.451247) | 2.063149 / 1.468490 (0.594659) | 0.696688 / 4.584777 (-3.888089) | 3.849370 / 3.745712 (0.103658) | 3.509495 / 5.269862 (-1.760367) | 1.923320 / 4.565676 (-2.642356) | 0.085554 / 0.424275 (-0.338721) | 0.012510 / 0.007607 (0.004903) | 0.535953 / 0.226044 (0.309909) | 5.365684 / 2.268929 (3.096755) | 2.686902 / 55.444624 (-52.757723) | 2.330922 / 6.876477 (-4.545554) | 2.353445 / 2.142072 (0.211373) | 0.878336 / 4.805227 (-3.926891) | 0.167296 / 6.500664 (-6.333368) | 0.064564 / 0.075469 (-0.010905) |

### 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) | 1.244696 / 1.841788 (-0.597091) | 15.027981 / 8.074308 (6.953673) | 14.545797 / 10.191392 (4.354405) | 0.147229 / 0.680424 (-0.533194) | 0.018007 / 0.534201 (-0.516194) | 0.446196 / 0.579283 (-0.133087) | 0.437418 / 0.434364 (0.003054) | 0.510732 / 0.540337 (-0.029606) | 0.594814 / 1.386936 (-0.792122) |

</details>
</details>

![](https://cml.dev/watermark.png#80eb8db74f49b7ee9c0f73a819c22177fabd61db "CML watermark")