ModuleNotFoundError: No module named 'apache_beam' for wikipedia datasets 
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['I sometimes also get this error with other languages of the same dataset:\r\n\r\n  File "/dara/libs/anaconda3/envs/code/lib/python3.7/site-packages/datasets-1.3.0-py3.7.egg/datasets/arrow_reader.py", line 322, in read_table\r\n    stream = stream_from(filename)\r\n  File "pyarrow/io.pxi", line 782, in pyarrow.lib.memory_map\r\n  File "pyarrow/io.pxi", line 743, in pyarrow.lib.MemoryMappedFile._open\r\n  File "pyarrow/error.pxi", line 122, in pyarrow.lib.pyarrow_internal_check_status\r\n  File "pyarrow/error.pxi", line 99, in pyarrow.lib.check_status\r\nOSError: Memory mapping file failed: Cannot allocate memory\r\n\r\n@lhoestq \r\n'
 "Hi ! Thanks for reporting\r\nSome wikipedia configurations do require the user to have `apache_beam` in order to parse the wikimedia data.\r\n\r\nOn the other hand regarding your second issue\r\n```\r\nOSError: Memory mapping file failed: Cannot allocate memory\r\n```\r\nI've never experienced this, can you open a new issue for this specific error and provide more details please ?\r\nFor example what script did you use to get this, what language did you use, what's your environment details (os, python version, pyarrow version).."]
Hi
I am trying to run run_mlm.py code [1] of huggingface with following "wikipedia"/ "20200501.aa"  dataset:

`python run_mlm.py     --model_name_or_path bert-base-multilingual-cased --dataset_name wikipedia     --dataset_config_name 20200501.aa     --do_train     --do_eval     --output_dir /tmp/test-mlm --max_seq_length 256
`

I am getting this error, but as per documentation, huggingface dataset provide processed version of this dataset and users can load it without requiring setup extra settings for apache-beam. could you help me please to load this dataset? 
Do you think I can run run_ml.py with this dataset? or anyway I could subsample and train the model? I greatly appreciate providing the processed version of all languages for this dataset, which allow the user to use them without setting up apache-beam,. thanks 

I really appreciate your help.
@lhoestq 

thanks.

[1] https://github.com/huggingface/transformers/blob/master/examples/language-modeling/run_mlm.py

error I get: 

```
>>> import datasets 
>>> datasets.load_dataset("wikipedia", "20200501.aa")
Downloading and preparing dataset wikipedia/20200501.aa (download: Unknown size, generated: Unknown size, post-processed: Unknown size, total: Unknown size) to /dara/temp/cache_home_2/datasets/wikipedia/20200501.aa/1.0.0/4021357e28509391eab2f8300d9b689e7e8f3a877ebb3d354b01577d497ebc63...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/dara/temp/libs/anaconda3/envs/codes/lib/python3.7/site-packages/datasets-1.3.0-py3.7.egg/datasets/load.py", line 746, in load_dataset
    use_auth_token=use_auth_token,
  File "/dara/temp/libs/anaconda3/envs/codes/lib/python3.7/site-packages/datasets-1.3.0-py3.7.egg/datasets/builder.py", line 573, in download_and_prepare
    dl_manager=dl_manager, verify_infos=verify_infos, **download_and_prepare_kwargs
  File "/dara/temp/libs/anaconda3/envs/codes/lib/python3.7/site-packages/datasets-1.3.0-py3.7.egg/datasets/builder.py", line 1099, in _download_and_prepare
    import apache_beam as beam
ModuleNotFoundError: No module named 'apache_beam'

```
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