Kokolipa/github-issues huggingface dataset:
Issue: Json loader fails if user-specified features don't match the json data fields order
State: closed
Labels: name: bug

If you do
```python
dataset = load_dataset("json", data_files=data_files, features=features)
```
Then depending on the order of the features in the json data field it fails:
```python
[...]
~/Desktop/hf/datasets/src/datasets/packaged_modules/json/json.py in _generate_tables(self, files)
     94             if self.config.schema:
     95                 # Cast allows str <-> int/float, while parse_option explicit_schema does NOT
---> 96                 pa_table = pa_table.cast(self.config.schema)
     97             yield i, pa_table
[...]
ValueError: Target schema's field names are not matching the table's field names: ['tokens', 'ner_tags'], ['ner_tags', 'tokens']
```

This is because one must first re-order the columns of the table to match the `self.config.schema` before calling cast.

One way to fix the `cast` would be to replace it with:
```python
# reorder the arrays if necessary + cast to schema
# we can't simply use .cast here because we may need to change the order of the columns
pa_table = pa.Table.from_arrays([pa_table[name] for name in schema.names], schema=schema)
```
Issue: Missing ClassLabel encoding in Json loader
State: closed
Labels: name: bug

Currently if you want to load a json dataset this way
```python
dataset = load_dataset("json", data_files=data_files, features=features)
```
Then if your features has ClassLabel types and if your json data needs class label encoding (i.e. if the labels in the json files are strings and not integers), then it would fail:
```python
[...]
~/Desktop/hf/datasets/src/datasets/packaged_modules/json/json.py in _generate_tables(self, files)
     94             if self.config.schema:
     95                 # Cast allows str <-> int/float, while parse_option explicit_schema does NOT
---> 96                 pa_table = pa_table.cast(self.config.schema)
     97             yield i, pa_table
[...]
ArrowInvalid: Failed to parse string: 'O' as a scalar of type int64
```

This is because it just tries to cast the string data to integers, without applying the mapping str->int first

The current workaround is to do instead
```python
dataset = load_dataset("json", data_files=data_files)
dataset = dataset.map(features.encode_example, features=features)
```
Issue: Allow model labels to be passed during task preparation
State: closed

Models have a config with label2id. And we have the same for datasets with the ClassLabel feature type. At one point either the model or the dataset must sync with the other. It would be great to do that on the dataset side.

For example for sentiment classification on amazon reviews with you could have these labels:
- "1 star", "2 stars", "3 stars", "4 stars", "5 stars"
- "1", "2", "3", "4", "5"

Some models may use the first set, while other models use the second set.

Here in the `TextClassification` class, the user can only specify one set of labels, while many models could actually be compatible but have different sets of labels. Should we allow users to pass a list of compatible labels sets ?

Then in terms of API, users could use `dataset.prepare_for_task("text-classification", labels=model.labels)` or something like that.

The label set could also be the same but not in the same order. For NLI for example, some models use `["neutral", "entailment", "contradiction"]` and some others use `["neutral", "contradiction", "entailment"]`, so we should take care of updating the order of the labels in the dataset to match the labels order of the model.

Let me know what you think ! This can be done in a future PR

_Originally posted by @lhoestq in https://github.com/huggingface/datasets/pull/2255#discussion_r632412792_

We now have the `align_labels_with_mapping` method in the API for this purpose.
Issue: `FaissIndex.save` throws error on GPU
State: closed
Labels: name: bug

## Describe the bug

After training an index with a factory string `OPQ16_128,IVF512,PQ32` on GPU, `.save_faiss_index` throws this error.

```
  File "index_wikipedia.py", line 119, in <module>
    data["train"].save_faiss_index("text_emb", index_save_path)
  File "/home/vlialin/miniconda3/envs/cat/lib/python3.8/site-packages/datasets/search.py", line 470, in save_faiss_index
    index.save(file)
  File "/home/vlialin/miniconda3/envs/cat/lib/python3.8/site-packages/datasets/search.py", line 334, in save
    faiss.write_index(index, str(file))
  File "/home/vlialin/miniconda3/envs/cat/lib/python3.8/site-packages/faiss/swigfaiss_avx2.py", line 5654, in write_index
    return _swigfaiss.write_index(*args)
RuntimeError: Error in void faiss::write_index(const faiss::Index*, faiss::IOWriter*) at /root/miniconda3/conda-bld/faiss-pkg_1613235005464/work/faiss/impl/index_write.cpp:453: don't know how to serialize this type of index
```

## Steps to reproduce the bug

Any dataset will do, I just selected a familiar one.

```python
import numpy as np
import datasets
INDEX_STR = "OPQ16_128,IVF512,PQ32"
INDEX_SAVE_PATH = "will_not_save.faiss"

data = datasets.load_dataset("Fraser/news-category-dataset", split=f"train[:10000]")

def encode(item):
    return {"text_emb": np.random.randn(768).astype(np.float32)}

data = data.map(encode)

data.add_faiss_index(column="text_emb", string_factory=INDEX_STR, train_size=10_000, device=0)
data.save_faiss_index("text_emb", INDEX_SAVE_PATH)
```

## Expected results
Saving the index

## Actual results
Error in void faiss::write_index(const faiss::Index*, faiss::IOWriter*) ... don't know how to serialize this type of index

## Environment info
- `datasets` version: 1.6.2
- Platform: Linux-4.15.0-142-generic-x86_64-with-glibc2.10
- Python version: 3.8.8
- PyTorch version (GPU?): 1.8.1+cu111 (True)
- Tensorflow version (GPU?): 2.2.0 (False)
- Using GPU in script?: Yes
- Using distributed or parallel set-up in script?: No


I will be proposing a fix in a couple of minutes

Just in case, this is a workaround that I use in my code and it seems to do the job.

```python
if use_gpu_index:
    data["train"]._indexes["text_emb"].faiss_index = faiss.index_gpu_to_cpu(data["train"]._indexes["text_emb"].faiss_index)
```
Issue: Add an API to access the language and pretty name of a dataset
State: closed
Labels: name: enhancement

It would be super nice to have an API to get some metadata of the dataset from the name and args passed to `load_dataset`. This way we could programmatically infer the language and the name of a dataset when creating model cards automatically in the Transformers examples scripts.

Hi ! With @bhavitvyamalik we discussed about having something like
```python
from datasets import load_dataset_card

dataset_card = load_dataset_card("squad")
print(dataset_card.metadata.pretty_name)
# Stanford Question Answering Dataset (SQuAD)
print(dataset_card.metadata.languages)
# ["en"]

```
What do you think ?

I don't know if you already have a way to load the model tags in `transformers` but we can agree on the API to have something consistent.

Also note that the pretty name would only be used to show users something prettier than a dataset id, but in the end the source of truth will stay the dataset id (here `squad`).

That works for me!

maybe use the hub-backed dataset_info method? (so there's only one parser of README.md metadata)?

What dataset_info method are you talking about @julien-c ? In `huggingface_hub` I can only see `model_info`.

hmm the equivalent method in `datasets` (which could go into `huggingface_hub` at some point)

Indeed, this info can now be fetched with `huggingface_hub.dataset_info`, so I think we can close this issue.
Issue: [Question] How to move and reuse preprocessed dataset? 
State: closed

Hi, I am training a gpt-2 from scratch using run_clm.py.

I want to move and reuse the preprocessed dataset (It take 2 hour to preprocess),

I tried to :

copy path_to_cache_dir/datasets to new_cache_dir/datasets
set export HF_DATASETS_CACHE="new_cache_dir/"
but the program still re-preprocess the whole dataset without loading cache.

I also tried to torch.save(lm_datasets, fw), but the saved file is only 14M.

What is the proper way to do this?

@lhoestq @LysandreJik


Hi :) Can you share with us the code you used ?


EDIT: from https://github.com/huggingface/transformers/issues/11665#issuecomment-838348291 I understand you're using the run_clm.py script. Can you share your logs ?


Also note that for the caching to work, you must reuse the exact same parameters as in the first run. Did you change any parameter ? The `preprocessing_num_workers` should also stay the same

> Also note that for the caching to work, you must reuse the exact same parameters as in the first run. Did you change any parameter ? The `preprocessing_num_workers` should also stay the same

I only changed the `preprocessing_num_workers` maybe it is the problem~ I will try again~
Issue: Is there a way to join multiple datasets in one?
State: open
Labels: name: enhancement

**Is your feature request related to a problem? Please describe.**
I need to join 2 datasets, one that is in the hub and another I've created from my files. Is there an easy way to join these 2? 

**Describe the solution you'd like**
Id like to join them with a merge or join method, just like pandas dataframes. 

**Additional context**
If you want to extend an existing dataset with more data, for example for training a language model, you need that functionality. I've not found it in the documentation.

Hi ! We don't have `join`/`merge` on a certain column as in pandas.
Maybe you can just use the [concatenate_datasets](https://huggingface.co/docs/datasets/package_reference/main_classes.html?highlight=concatenate#datasets.concatenate_datasets) function.


Hi! You can use `datasets_sql` for that now. As of recently, PyArrow also supports querying tables via Substrait, so I think we can start adding these methods to the API soon.
Issue: Columns are removed before or after map function applied?
State: open
Labels: name: bug

## Describe the bug
According to the documentation when applying map function the [remove_columns ](https://huggingface.co/docs/datasets/processing.html#removing-columns) will be removed after they are passed to the function, but in the [source code](https://huggingface.co/docs/datasets/package_reference/main_classes.html#datasets.Dataset.map) it's documented that they are removed before applying function. I thinks the source code doc is more accurate, right?





Hi! Columns are removed **after** applying the function and **before** updating the examples with the function's output (as per the docs [here](https://huggingface.co/docs/datasets/package_reference/main_classes#datasets.Dataset.map.remove_columns)). I agree the docs on this should be more clear.
Issue: NonMatchingChecksumError for web_of_science dataset
State: closed
Labels: name: bug

NonMatchingChecksumError when trying to download the web_of_science dataset. 

>NonMatchingChecksumError: Checksums didn't match for dataset source files:
['https://data.mendeley.com/datasets/9rw3vkcfy4/6/files/c9ea673d-5542-44c0-ab7b-f1311f7d61df/WebOfScience.zip?dl=1']

Setting `ignore_verfications=True` results in OSError.

>OSError: Cannot find data file. 
Original error:
[Errno 20] Not a directory: '/root/.cache/huggingface/datasets/downloads/37ab2c42f50d553c1d0ea432baca3e9e11fedea4aeec63a81e6b7e25dd10d4e7/WOS5736/X.txt'

```python
dataset = load_dataset('web_of_science', 'WOS5736')
```
There are 3 data instances and they all don't work. 'WOS5736', 'WOS11967', 'WOS46985'

datasets 1.6.2
python 3.7.10
Ubuntu 18.04.5 LTS

I've raised a PR for this. Should work with `dataset = load_dataset("web_of_science", "WOS11967", ignore_verifications=True)`once it gets merged into the main branch. Thanks for reporting this!
Issue: Index error in Dataset.map
State: closed
Labels: name: bug

The following code, if executed on master, raises an IndexError (due to overflow):
```python
>>> from datasets import *
>>> d = load_dataset("bookcorpus", split="train")
Reusing dataset bookcorpus (C:\Users\Mario\.cache\huggingface\datasets\bookcorpus\plain_text\1.0.0\44662c4a114441c35200992bea923b170e6f13f2f0beb7c14e43759cec498700)
2021-05-08 21:23:46.859818: I tensorflow/stream_executor/platform/default/dso_loader.cc:48] Successfully opened dynamic library cudart64_101.dll
>>> d.map(lambda ex: ex)
  0%|▎                                                                    | 289430/74004228 [00:13<58:41, 20935.33ex/s]c:\users\mario\desktop\projects\datasets-1\src\datasets\table.py:84: RuntimeWarning: overflow encountered in int_scalars
  k = i + ((j - i) * (x - arr[i]) // (arr[j] - arr[i]))
  0%|▎                                                                    | 290162/74004228 [00:13<59:11, 20757.23ex/s]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\arrow_dataset.py", line 1498, in map
    new_fingerprint=new_fingerprint,
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\arrow_dataset.py", line 174, in wrapper
    out: Union["Dataset", "DatasetDict"] = func(self, *args, **kwargs)
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\fingerprint.py", line 340, in wrapper
    out = func(self, *args, **kwargs)
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\arrow_dataset.py", line 1799, in _map_single
    for i, example in enumerate(pbar):
  File "C:\Users\Mario\Anaconda3\envs\hf-datasets\lib\site-packages\tqdm\std.py", line 1133, in __iter__
    for obj in iterable:
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\arrow_dataset.py", line 1145, in __iter__
    format_kwargs=format_kwargs,
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\arrow_dataset.py", line 1337, in _getitem
    pa_subtable = query_table(self._data, key, indices=self._indices if self._indices is not None else None)
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\formatting\formatting.py", line 368, in query_table
    pa_subtable = _query_table(table, key)
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\formatting\formatting.py", line 79, in _query_table
    return table.fast_slice(key % table.num_rows, 1)
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\table.py", line 128, in fast_slice
    i = _interpolation_search(self._offsets, offset)
  File "c:\users\mario\desktop\projects\datasets-1\src\datasets\table.py", line 91, in _interpolation_search
    raise IndexError(f"Invalid query '{x}' for size {arr[-1] if len(arr) else 'none'}.")
IndexError: Invalid query '290162' for size 74004228.
```
Tested on Windows, can run on Linux if needed.

EDIT:
It seems like for this to happen, the default NumPy dtype has to be np.int32.
Issue: Add Topical-Chat
State: open
Labels: name: dataset request

## Adding a Dataset
- **Name:** Topical-Chat
- **Description:** a knowledge-grounded human-human conversation dataset where the underlying knowledge spans 8 broad topics and conversation partners don’t have explicitly defined roles
- **Paper:** https://www.isca-speech.org/archive/Interspeech_2019/pdfs/3079.pdf
- **Data:** https://github.com/alexa/Topical-Chat
- **Motivation:** Good quality, knowledge-grounded dataset that spans a broad range of topics

Instructions to add a new dataset can be found [here](https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md).
Issue: Allow passing `desc` to `tqdm` in `Dataset.map()`
State: closed
Labels: name: enhancement

name: good first issue

It's normal to have many `map()` calls, and some of them can take a few minutes,
it would be nice to have a description on the progress bar.

Alternative solution:
Print the description before/after the `map()` call.

Hi @lhoestq,
Should we change `desc` in [pbar](https://github.com/huggingface/datasets/blob/81fcf88172ed5e3026ef68aed4c0ec6980372333/src/datasets/arrow_dataset.py#L1860) to something meaningful?

I think the user could pass the `desc` parameter to `map` so that it can be displayed in the tqdm progress bar, as suggested by @cccntu.

When there's no multiprocessing, the `desc` of the progress bar could be the `desc` passed by the user.
In multiprocessing, we were already using a `desc` equal to `"#" + str(rank)`.
We can change it to be `(desc or "") + "#" + str(rank)` instead.

In the end, since both `desc` and `rank` could be None, we can have:
```python
pbar_desc = (desc or "") + "#" + str(rank) if rank is not None else desc
```

Finally let's remember that if we add `desc` as a new parameter to `map`, we should add it to the `ignore_kwargs` list of the `@fingerprint_transform` decorator of `Dataset._map_single` since we don't want this parameter to affect the fingerprint of the resulting dataset.
Issue: A syntax error in example
State: closed
Labels: name: bug

![image](https://user-images.githubusercontent.com/6883957/117315905-b47a5c00-aeba-11eb-91eb-b2a4a0212a56.png)

Sorry to report with an image, I can't find the template source code of this snippet.

cc @beurkinger but I think this has been fixed internally and will soon be updated right ?

This issue has been fixed.
Issue: load_dataset("timit_asr") gives back duplicates of just one sample text
State: closed
Labels: name: bug

## Describe the bug
When you look up on key ["train"] and then ['text'], you get back a list  with just one sentence duplicated 4620 times. Namely, the sentence "Would such an act of refusal be useful?". Similarly when you look up ['test'] and then ['text'], the list is one sentence repeated "The bungalow was pleasantly situated near the shore." 1680 times. 

I tried to work around the issue by downgrading to datasets version 1.3.0, inspired by [this post](https://www.gitmemory.com/issue/huggingface/datasets/2052/798904836) and removing the entire huggingface directory from ~/.cache, but I still get the same issue.  

## Steps to reproduce the bug
```python
from datasets import load_dataset
timit = load_dataset("timit_asr")
print(timit['train']['text'])
print(timit['test']['text'])
```

## Expected Result
Rows of diverse text, like how it is shown in the [wav2vec2.0 tutorial](https://colab.research.google.com/github/patrickvonplaten/notebooks/blob/master/Fine_tuning_Wav2Vec2_for_English_ASR.ipynb)
<img width="485" alt="Screen Shot 2021-05-05 at 9 09 57 AM" src="https://user-images.githubusercontent.com/33647474/117146094-d9b77f00-ad81-11eb-8306-f281850c127a.png">


## Actual results
Rows of repeated text.
<img width="319" alt="Screen Shot 2021-05-05 at 9 11 53 AM" src="https://user-images.githubusercontent.com/33647474/117146231-f8b61100-ad81-11eb-834a-fc10410b0c9c.png">


## Versions
- Datasets: 1.3.0
- Python: 3.9.1
- Platform: macOS-11.2.1-x86_64-i386-64bit}


Upgrading datasets to version 1.6 fixes the issue

This bug was fixed in #1995. Upgrading the `datasets` should work! 

Thanks @ekeleshian for having reported.

I am closing this issue once that you updated `datasets`. Feel free to reopen it if the problem persists.
Issue: [api request] API to obtain "dataset_module" dynamic path?
State: closed
Labels: name: enhancement

**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is.

This is an awesome library. 

It seems like the dynamic module path in this library has broken some of hyperparameter tuning functionality: https://discuss.huggingface.co/t/using-hyperparameter-search-in-trainer/785/34

This is because Ray will spawn new processes, and each process will load modules by path. However, we need to explicitly inform Ray to load the right modules, or else it will error upon import. 

I'd like an API to obtain the dynamic paths. This will allow us to support this functionality in this awesome library while being future proof.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

`datasets.get_dynamic_paths -> List[str]` will be sufficient for my use case.

By offering this API, we will be able to address the following issues (by patching the ray integration sufficiently):

https://github.com/huggingface/blog/issues/106
https://github.com/huggingface/transformers/issues/11565
https://discuss.huggingface.co/t/using-hyperparameter-search-in-trainer/785/34
https://discuss.huggingface.co/t/using-hyperparameter-search-in-trainer/785/35



Hi @richardliaw, 

First, thanks for the compliments.

In relation with your request, currently, the dynamic modules path is obtained this way:
```python
from datasets.load import init_dynamic_modules, MODULE_NAME_FOR_DYNAMIC_MODULES

dynamic_modules_path = init_dynamic_modules(MODULE_NAME_FOR_DYNAMIC_MODULES)
```

Let me know if it is OK for you this way. 

I could set `MODULE_NAME_FOR_DYNAMIC_MODULES` as default value, so that you could instead obtain the path with:
```
dynamic_modules_path = datasets.load.init_dynamic_modules()
```

Hi @albertvillanova, the default value proposal seems great :) Looking forward to this!

I like the idea as well ! thanks @albertvillanova 

Hi @richardliaw, the feature is on the master branch and will be included in the next release in a couple of weeks.

awesome work @albertvillanova !
Issue: Incorrect version specification for pyarrow
State: closed
Labels: name: bug

## Describe the bug
The pyarrow dependency is incorrectly specified in setup.py file, in [this line](https://github.com/huggingface/datasets/blob/3a3e5a4da20bfcd75f8b6a6869b240af8feccc12/setup.py#L77).
Also as a snippet:
```python
 "pyarrow>=1.0.0<4.0.0",
```

## Steps to reproduce the bug
```bash
 pip install "pyarrow>=1.0.0<4.0.0"
```

## Expected results
It is expected to get a pyarrow version between 1.0.0 (inclusive) and 4.0.0 (exclusive).

## Actual results
pip ignores the specified versions since there is a missing comma between the lower and upper limits. Therefore, pip installs the latest pyarrow version from PYPI, which is 4.0.0.
This is especially problematic since "conda env export" fails due to incorrect version specification. Here is the conda error as well:
```bash
conda env export
InvalidVersionSpec: Invalid version '1.0.0<4.0.0': invalid character(s)
```


## Fix suggestion
Put a comma between the version limits which means replacing the line in setup.py file with the following:
```python
 "pyarrow>=1.0.0,<4.0.0",
```

## Versions
Paste the output of the following code:
```python
- Datasets: 1.6.2
- Python: 3.7.10 (default, Feb 26 2021, 18:47:35) 
[GCC 7.3.0]
- Platform: Linux-5.4.0-42-generic-x86_64-with-debian-buster-sid
```


Fixed by #2317.
Issue: Add VoxPopuli
State: closed
Labels: name: dataset request

name: speech

## Adding a Dataset
- **Name:** Voxpopuli
- **Description:** VoxPopuli is raw data is collected from 2009-2020 European Parliament event recordings
- **Paper:** https://arxiv.org/abs/2101.00390
- **Data:** https://github.com/facebookresearch/voxpopuli
- **Motivation:** biggest unlabeled speech dataset

**Note**: Since the dataset is so huge, we should only add the config `10k` in the beginning.

Instructions to add a new dataset can be found [here](https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md).


I'm happy to take this on:) One question: The original unlabelled data is stored unsegmented (see e.g. https://github.com/facebookresearch/voxpopuli/blob/main/voxpopuli/get_unlabelled_data.py#L30), but segmenting the audio in the dataset would require a dependency on something like soundfile or torchaudio. An alternative could be to provide the segments start and end times as a Sequence and then it's up to the user to perform the segmentation on-the-fly if they wish?

Hey @jfainberg,

This sounds great! I think adding a dependency would not be a big problem, however automatically segmenting the data probably means that it would take a very long time to do:

```python
dataset = load_dataset("voxpopuli", "french")
```

=> so as a start I think your option 2 is the way to go!

@polinaeterna VoxPopuli is available [here](https://huggingface.co/datasets/facebook/voxpopuli), so we can close this issue, right?


@mariosasko yes, sure, closing it
Issue: My iPhone
State: closed

## Adding a Dataset
- **Name:** *name of the dataset*
- **Description:** *short description of the dataset (or link to social media or blog post)*
- **Paper:** *link to the dataset paper if available*
- **Data:** *link to the Github repository or current dataset location*
- **Motivation:** *what are some good reasons to have this dataset*

Instructions to add a new dataset can be found [here](https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md).
Issue: 1
State: closed
Labels: name: dataset request

## Adding a Dataset
- **Name:** *name of the dataset*
- **Description:** *short description of the dataset (or link to social media or blog post)*
- **Paper:** *link to the dataset paper if available*
- **Data:** *link to the Github repository or current dataset location*
- **Motivation:** *what are some good reasons to have this dataset*

Instructions to add a new dataset can be found [here](https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md).
Issue: Slow #0 when using map to tokenize.
State: open

Hi, _datasets_ is really amazing! I am following [run_mlm_no_trainer.py](url) to pre-train BERT, and it uses `tokenized_datasets = raw_datasets.map(
            tokenize_function,
            batched=True,
            num_proc=args.preprocessing_num_workers,
            remove_columns=column_names,
            load_from_cache_file=not args.overwrite_cache,
        )` to tokenize by multiprocessing. However, I have found that when `num_proc`>1，the process _#0_ is much slower than others.
It looks like this:
![image](https://user-images.githubusercontent.com/31714566/116665555-81246280-a9cc-11eb-8a37-6e608ab310d0.png)
It takes more than 12 hours for #0, while others just about half an hour. Could anyone tell me it is normal or not, and is there any methods to speed up it?


Hi ! Have you tried other values for `preprocessing_num_workers` ? Is it always process 0 that is slower ?
There are no difference between process 0 and the others except that it processes the first shard of the dataset.

Hi, I have found the reason of it. Before using the map function to tokenize the data, I concatenate the wikipedia and bookcorpus first, like this:
```if args.dataset_name1 is not None:
        dataset1 = load_dataset(args.dataset_name1, args.dataset_config_name1, split="train")
        dataset1 = dataset1.remove_columns('title')
        if args.dataset_name2 is not None:
            dataset2 = load_dataset(args.dataset_name2, args.dataset_config_name2,split="train")
            assert dataset1.features.type == dataset2.features.type, str(dataset1.features.type)+';'+str(dataset2.features.type)
           datasets12 = concatenate_datasets([dataset1, dataset2], split='train')
```
When I just use one datasets, e.g. wikipedia, the problem seems no longer exist:
![image](https://user-images.githubusercontent.com/31714566/116967059-13d24380-ace4-11eb-8d14-b7b9c9a275cc.png)

Bookcorpus has more row numbers than Wikipedia, however, it takes much more time to process each batch of wiki than that of bookcorpus. When we first concatenate two datasets and then use _map_ to process the concatenated datasets,  e.g. `num_proc=5`, process 0 has to process all of the wikipedia data, causing the problem that #0 takes a longer time to finish the job. 

The problem is caused by the different characteristic of different datasets. One solution might be using _map_ first to process two datasets seperately, then concatenate the tokenized and processed datasets before input to the `Dataloader`.



That makes sense ! You can indeed use `map` on both datasets separately and then concatenate.
Another option is to concatenate, then shuffle, and then `map`.
Issue: Load_dataset for local CSV files
State: closed
Labels: name: bug

The method load_dataset fails to correctly load a dataset from csv. 

Moreover, I am working on a token-classification task ( POS tagging) , where each row in my CSV contains two columns each of them having a list of strings.
row example:
```tokens  |  labels
['I' , 'am', 'John']  |  ['PRON', 'AUX', 'PROPN' ] 
```
The method, loads each list as a string:  (i.g "['I' , 'am', 'John']").
To solve this issue, I copied the Datasets.Features, created Sequence types ( instead of Value)  and tried to cast the features type
```
new_features['tokens'] = Sequence(feature=Value(dtype='string', id=None))
new_features['labels'] = Sequence(feature=ClassLabel(num_classes=len(tag2idx), names=list(unique_tags)))
dataset = dataset.cast(new_features)
```
but I got the following error 
```
ArrowNotImplementedError: Unsupported cast from string to list using function cast_list
```
Moreover, I tried to set feature parameter in load_dataset method, to my new_features, but this fails as well.
How can this be solved ?

Hi,

this is not a standard CSV file (requires additional preprocessing) so I wouldn't label this as s bug. You could parse the examples with the regex module or the string API to extract the data, but the following approach is probably the easiest (once you load the data):
```python
import ast
# load the dataset and copy the features
def process(ex):
    return {"tokens": ast.literal_eval(ex["tokens"]), "labels": ast.literal_eval(ex["labels"])}
dataset = dataset.map(process, features=new_features)
```


Hi,

Thanks for the reply.
I  have already used  ```ast.literal_eval``` to evaluate the string into list, but I was getting another error:
```
ArrowInvalid: Could not convert X with type str: tried to convert to int
```
Why this happens ? Should labels be mapped to their ids and use int instead of str ?

Yes, just map the labels to their ids.
Issue: SNLI dataset has labels of -1 
State: closed

There are a number of rows with a label of -1 in the SNLI dataset. The dataset descriptions [here](https://nlp.stanford.edu/projects/snli/) and [here](https://github.com/huggingface/datasets/tree/master/datasets/snli) don't list  -1 as a label possibility, and neither does the dataset viewer. As examples, see index 107 or 124 of the test set.

It isn't clear what these labels mean. I found a [line of code](https://github.com/huggingface/datasets/blob/80e59ef178d3bb2090d091bc32315c655eb0633d/datasets/snli/snli.py#L94) that seems to put them in but it seems still unclear why they are there. The current workaround is to just drop the rows from any model being trained. 

Perhaps the documentation should be updated.

Hi @puzzler10, 
Those examples where `gold_label` field was empty, -1 label was alloted to it. In order to remove it you can filter the samples from train/val/test splits. Here's how you can drop those rows from the dataset:
`dataset = load_dataset("snli")`
`dataset_test_filter = dataset['test'].filter(lambda example: example['label'] != -1)`

I agree it should have been mentioned in the documentation. I'll raise a PR regarding the same. Thanks for pointing out!
Issue: Bug in Dataset.class_encode_column
State: closed
Labels: name: bug

## Describe the bug

All the rest of the columns except the one passed to `Dataset.class_encode_column` are discarded.

## Expected results

All the original columns should be kept.

This needs regression tests.


This has been fixed in this commit: https://github.com/huggingface/datasets/pull/2254/commits/88676c930216cd4cc31741b99827b477d2b46cb6

It was introduced in #2246 : using map with `input_columns` doesn't return the other columns anymore
Issue: Synchronize table metadata with features
State: closed
Labels: name: enhancement

**Is your feature request related to a problem? Please describe.**

As pointed out in this [comment](https://github.com/huggingface/datasets/pull/2145#discussion_r621326767):
> Metadata stored in the schema is just a redundant information regarding the feature types.
It is used when calling Dataset.from_file to know which feature types to use.
These metadata are stored in the schema of the pyarrow table by using `update_metadata_with_features`.
However this something that's almost never tested properly.

**Describe the solution you'd like**

We should find a way to always make sure that the metadata (in `self.data.schema.metadata`) are synced with the actual feature types (in `self.info.features`).

See PR #2274
Issue: Running `datase.map` with `num_proc > 1` uses a lot of memory
State: closed
Labels: name: bug

## Describe the bug
Running `datase.map` with `num_proc > 1`  leads to a tremendous memory usage that requires swapping on disk and it becomes very slow.

## Steps to reproduce the bug
```python
from datasets import load_dataset

dstc8_datset = load_dataset("roskoN/dstc8-reddit-corpus", keep_in_memory=False)


def _prepare_sample(batch):
    return {"input_ids": list(), "attention_mask": list()}


for split_name, dataset_split in list(dstc8_datset.items()):
    print(f"Processing {split_name}")
    encoded_dataset_split = dataset_split.map(
        function=_prepare_sample,
        batched=True,
        num_proc=4,
        remove_columns=dataset_split.column_names,
        batch_size=10,
        writer_batch_size=10,
        keep_in_memory=False,
    )
    print(encoded_dataset_split)

    path = f"./data/encoded_{split_name}"

    encoded_dataset_split.save_to_disk(path)
```

## Expected results
Memory usage should stay within reasonable boundaries.


## Actual results
This is htop-output from running the provided script.

![image](https://user-images.githubusercontent.com/8143425/115954836-66954980-a4f3-11eb-8340-0153bdc3a475.png)

## Versions
```
- Datasets: 1.6.0
- Python: 3.8.8 (default, Apr 13 2021, 19:58:26)
[GCC 7.3.0]
- Platform: Linux-4.19.128-microsoft-standard-x86_64-with-glibc2.10
```
Running on WSL2


Thanks for reporting ! We are working on this and we'll do a patch release very soon.

We did a patch release to fix this issue.
It should be fixed in the new version 1.6.1

Thanks again for reporting and for the details :)
Issue: while running run_qa.py, ran into a value error
State: open

command:

python3 run_qa.py   --model_name_or_path hyunwoongko/kobart    --dataset_name squad_kor_v2   --do_train   --do_eval   --per_device_train_batch_size 8   --learning_rate 3e-5   --num_train_epochs 3   --max_seq_length 512   --doc_stride 128   --output_dir /tmp/debug_squad/

error: 

ValueError: External features info don't match the dataset:
Got
{'id': Value(dtype='string', id=None), 'title': Value(dtype='string', id=None), 'context': Value(dtype='string', id=None), 'question': Value(dtype='string', id=None), 'answer': {'text': Value(dtype='string', id=None), 'answer_start': Value(dtype='int32', id=None), 'html_answer_start': Value(dtype='int32', id=None)}, 'url': Value(dtype='string', id=None), 'raw_html': Value(dtype='string', id=None)}
with type
struct<answer: struct<text: string, answer_start: int32, html_answer_start: int32>, context: string, id: string, question: string, raw_html: string, title: string, url: string>

but expected something like
{'answer': {'answer_start': Value(dtype='int32', id=None), 'html_answer_start': Value(dtype='int32', id=None), 'text': Value(dtype='string', id=None)}, 'context': Value(dtype='string', id=None), 'id': Value(dtype='string', id=None), 'question': Value(dtype='string', id=None), 'raw_html': Value(dtype='string', id=None), 'title': Value(dtype='string', id=None), 'url': Value(dtype='string', id=None)}
with type
struct<answer: struct<answer_start: int32, html_answer_start: int32, text: string>, context: string, id: string, question: string, raw_html: string, title: string, url: string>

I didn't encounter this error 4 hours ago. any solutions for this kind of issue?
looks like gained dataset format refers to 'Data Fields', while expected refers to 'Data Instances'.
Issue: Map is slow and processes batches one after another
State: closed
Labels: name: bug

## Describe the bug

I have a somewhat unclear bug to me, where I can't figure out what the problem is. The code works as expected on a small subset of my dataset (2000 samples) on my local machine, but when I execute the same code with a larger dataset (1.4 million samples) this problem occurs. Thats why I can't give exact steps to reproduce, I'm sorry. 

I process a large dataset in a two step process. I first call map on a dataset I load from disk and create a new dataset from it. This works like expected and `map` uses all workers I started it with. Then I process the dataset created by the first step, again with `map`, which is really slow and starting only one or two process at a time. Number of processes is the same for both steps.

pseudo code:
```python
ds = datasets.load_from_disk("path")
new_dataset = ds.map(work, batched=True, ...)  # fast uses all processes
final_dataset = new_dataset.map(work2, batched=True, ...)  # slow starts one process after another
```

## Expected results
Second stage should be as fast as the first stage.

## Versions
Paste the output of the following code:
- Datasets: 1.5.0
- Python: 3.8.8 (default, Feb 24 2021, 21:46:12)
- Platform: Linux-5.4.0-60-generic-x86_64-with-glibc2.10    

Do you guys have any idea? Thanks a lot!

Hi @villmow, thanks for reporting.

Could you please try with the Datasets version 1.6? We released it yesterday and it fixes some issues about the processing speed. You can see the fix implemented by @lhoestq here: #2122.

Once you update Datasets, please confirm if the problem persists.

Hi @albertvillanova, thanks for the reply. I just tried the new version and the problem still persists. 

Do I need to rebuild the saved dataset (which I load from disk) with the 1.6.0 version of datasets? My script loads this dataset and creates new datasets from it. I tried it without rebuilding.

See this short video of what happens. It does not create all processes at the same time:

https://user-images.githubusercontent.com/2743060/115720139-0da3a500-a37d-11eb-833a-9bbacc70868d.mp4



There can be a bit of delay between the creations of the processes but this delay should be the same for both your `map` calls. We should look into this.
Also if you hav some code that reproduces this issue on google colab that'd be really useful !

Regarding the speed differences:
This looks like a similar issue as https://github.com/huggingface/datasets/issues/1992 who is experiencing the same speed differences between processes.
This is a known bug that we are investigating. As of now I've never managed to reproduce it on my machine so it's pretty hard for me to find where this issue comes from.


Upgrade to 1.6.1 solved my problem somehow. I did not change any of my code, but now it starts all processes around the same time.

Nice ! I'm glad this works now.
Closing for now, but feel free to re-open if you experience this issue again.
Issue: Link to datasets viwer on Quick Tour page returns "502 Bad Gateway"
State: closed
Labels: name: bug

Link to datasets viwer (https://huggingface.co/datasets/viewer/)  on Quick Tour page  (https://huggingface.co/docs/datasets/quicktour.html) returns "502 Bad Gateway"

The same error with https://huggingface.co/datasets/viewer/?dataset=glue&config=mrpc 

This should be fixed now!

cc @srush
Issue: Request to add StrategyQA dataset
State: open
Labels: name: dataset request

## Request to add StrategyQA dataset
- **Name:** StrategyQA
- **Description:** open-domain QA [(project page)](https://allenai.org/data/strategyqa)
- **Paper:** [url](https://arxiv.org/pdf/2101.02235.pdf)
- **Data:** [here](https://allenai.org/data/strategyqa)
- **Motivation:** uniquely-formulated dataset that also includes a question-decomposition breakdown and associated Wikipedia annotations for each step. Good for multi-hop reasoning modeling.
Issue: `xnli` dataset creating a tuple key while yielding instead of `str` or `int`
State: closed

When using  `ds = datasets.load_dataset('xnli', 'ar')`, the dataset generation script uses the following section of code in the egging, which yields a tuple key instead of the specified `str` or `int` key:
https://github.com/huggingface/datasets/blob/56346791aed417306d054d89bd693d6b7eab17f7/datasets/xnli/xnli.py#L196

Since, community datasets in Tensorflow Datasets also use HF datasets, this causes a Tuple key error while loading HF's `xnli` dataset. 
I'm up for sending a fix for this, I think we can simply use `file_idx + "_" + row_idx` as a unique key instead of a tuple.

Hi ! Sure sounds good. Also if you find other datasets that use tuples instead of str/int, you can also fix them !
thanks :)

@lhoestq I have sent a PR for fixing the issue. Would be great if you could have a look! Thanks!
Issue: load_metric error: module 'datasets.utils.file_utils' has no attribute 'add_start_docstrings'
State: closed
Labels: name: bug

I'm having the same problem as [Notebooks issue 10](https://github.com/huggingface/notebooks/issues/10) on datasets 1.2.1, and it seems to be an issue with the datasets package.

```python
>>> from datasets import load_metric
>>> metric = load_metric("glue", "sst2")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/ext3/miniconda3/lib/python3.8/site-packages/datasets-1.2.1-py3.8.egg/datasets/load.py", line 502, in load_metric
  File "/ext3/miniconda3/lib/python3.8/site-packages/datasets-1.2.1-py3.8.egg/datasets/load.py", line 66, in import_main_class
  File "/ext3/miniconda3/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/ns4008/.cache/huggingface/modules/datasets_modules/metrics/glue/e4606ab9804a36bcd5a9cebb2cb65bb14b6ac78ee9e6d5981fa679a495dd55de/glue.py", line 105, in <module>
    @datasets.utils.file_utils.add_start_docstrings(_DESCRIPTION, _KWARGS_DESCRIPTION)
AttributeError: module 'datasets.utils.file_utils' has no attribute 'add_start_docstrings'
```

Hi @nsaphra, thanks for reporting.

This issue was fixed in `datasets` version 1.3.0. Could you please update `datasets` and tell me if the problem persists?
```shell
pip install -U datasets
```

There might be a bug in the conda version of `datasets` 1.2.1 where the datasets/metric scripts are downloaded from `master` instead of the `1.2.1` repo.

You can try setting the env var `HF_SCRIPTS_VERSION="1.2.1"` as a workaround. Let me know if that helps.

I just faced the same issue. I was using 1.2.1 from conda and received the same AttributeError complaining about 'add_start_docstrings'. Uninstalling the conda installed datasets and then installing the latest datasets (version 1.5.0) using pip install solved the issue for me. I don't like mixing up conda and pip installs in the same environments but this will have to do for now, until 1.5.0 is made available through conda.

Yep, seems to have fixed things! The conda package could really do with an update. Thanks!
Issue: Can't reach "https://storage.googleapis.com/illuin/fquad/train.json.zip" when trying to load fquad dataset
State: closed

I'm trying to load the [fquad dataset](https://huggingface.co/datasets/fquad) by running: 

```Python
fquad = load_dataset("fquad")
```

which produces the following error:

```
Using custom data configuration default

Downloading and preparing dataset fquad/default (download: 3.14 MiB, generated: 6.62 MiB, post-processed: Unknown size, total: 9.76 MiB) to /root/.cache/huggingface/datasets/fquad/default/0.1.0/778dc2c85813d05ddd0c17087294d5f8f24820752340958070876b677af9f061...

---------------------------------------------------------------------------

ConnectionError                           Traceback (most recent call last)

<ipython-input-48-a2721797e23b> in <module>()
----> 1 fquad = load_dataset("fquad")

11 frames

/usr/local/lib/python3.7/dist-packages/datasets/utils/file_utils.py in get_from_cache(url, cache_dir, force_download, proxies, etag_timeout, resume_download, user_agent, local_files_only, use_etag, max_retries, use_auth_token)
    614             raise FileNotFoundError("Couldn't find file at {}".format(url))
    615         _raise_if_offline_mode_is_enabled(f"Tried to reach {url}")
--> 616         raise ConnectionError("Couldn't reach {}".format(url))
    617 
    618     # Try a second time

ConnectionError: Couldn't reach https://storage.googleapis.com/illuin/fquad/train.json.zip
```

Does anyone know why that is and how to fix it? 

Hi ! Apparently the data are not available from this url anymore. We'll replace it with the new url when it's available

I saw this on their website when we request to download the dataset:
![image](https://user-images.githubusercontent.com/19718818/114879600-fa458680-9e1e-11eb-9e05-f0963d68ff0f.png)

Can we still request them link for the dataset and make a PR? @lhoestq @yjernite 

I've contacted Martin (first author of the fquad paper) regarding a possible new url. Hopefully we can get one soon !

They now made a website to force people who want to use the dataset for commercial purposes to seek a commercial license from them ...

The script has been adopted to support manual download from the website, so I'm closing this issue.
Issue: Getting checksum error when trying to load lc_quad dataset
State: closed

I'm having issues loading the [lc_quad](https://huggingface.co/datasets/fquad) dataset by running:

```Python
lc_quad = load_dataset("lc_quad")
```

which is giving me the following error:

``` 
Using custom data configuration default

Downloading and preparing dataset lc_quad/default (download: 3.69 MiB, generated: 19.77 MiB, post-processed: Unknown size, total: 23.46 MiB) to /root/.cache/huggingface/datasets/lc_quad/default/2.0.0/5a98fe174603f5dec6df07edf1c2b4d2317210d2ad61f5a393839bca4d64e5a7...

---------------------------------------------------------------------------

NonMatchingChecksumError                  Traceback (most recent call last)

<ipython-input-42-404ace83f73c> in <module>()
----> 1 lc_quad = load_dataset("lc_quad")

3 frames

/usr/local/lib/python3.7/dist-packages/datasets/utils/info_utils.py in verify_checksums(expected_checksums, recorded_checksums, verification_name)
     37     if len(bad_urls) > 0:
     38         error_msg = "Checksums didn't match" + for_verification_name + ":\n"
---> 39         raise NonMatchingChecksumError(error_msg + str(bad_urls))
     40     logger.info("All the checksums matched successfully" + for_verification_name)
     41 

NonMatchingChecksumError: Checksums didn't match for dataset source files:
['https://github.com/AskNowQA/LC-QuAD2.0/archive/master.zip']
```

Does anyone know why this could be and how I fix it? 

Hi,

I've already opened a PR with the fix. If you are in a hurry, just build the project from source and run:
```bash
datasets-cli test datasets/lc_quad --save_infos --all_configs --ignore_verifications
```



Ah sorry, I tried searching but couldn't find any related PR. 

Thank you!