ModuleNotFoundError: No module named 'apache_beam', when specific languages.
the #2037 doesn't solve my problem directly, but I found the point!

https://github.com/huggingface/datasets/blob/349ac4398a3bcae6356f14c5754483383a60e8a4/datasets/wikipedia/wikipedia.py#L523
this `beam.transforms.Reshuffle()` cause the memory error.

it makes sense if I consider the shuffle means. Beam's reshuffle seems need put all data in memory.
Previously I doubt that this line causes error, but at that time another bug showed in #2037 made error, so I can't found it.

Anyway, I comment out this line, and run load_dataset, then it works!

```python
wiki = datasets.load_dataset(
    "./wikipedia.py",
    cache_dir="./datasets",
    beam_runner="DirectRunner",
    language="ja",
    date="20210120",
)["train"]
```
![image](https://user-images.githubusercontent.com/6331508/112283369-6a9f3300-8ccb-11eb-82e5-827bf7fddfb9.png)

Dataset has already shuffle function. https://github.com/huggingface/datasets/blob/349ac4398a3bcae6356f14c5754483383a60e8a4/src/datasets/arrow_dataset.py#L2069
So, though I don't know it's difference correctly, but I think Beam's reshuffle isn't be needed. How do you think?
```py
import datasets
wiki = datasets.load_dataset('wikipedia', '20200501.ja', cache_dir='./datasets')
```
then `ModuleNotFoundError: No module named 'apache_beam'` happend.

The error doesn't appear when it's '20200501.en'.
I don't know Apache Beam, but according to #498 it isn't necessary when it's saved to local. is it correct?
ModuleNotFoundError: No module named 'apache_beam', when specific languages. 
 ```py
import datasets
wiki = datasets.load_dataset('wikipedia', '20200501.ja', cache_dir='./datasets')
```
then `ModuleNotFoundError: No module named 'apache_beam'` happend.

The error doesn't appear when it's '20200501.en'.
I don't know Apache Beam, but according to #498 it isn't necessary when it's saved to local. is it correct? 
 the #2037 doesn't solve my problem directly, but I found the point!

https://github.com/huggingface/datasets/blob/349ac4398a3bcae6356f14c5754483383a60e8a4/datasets/wikipedia/wikipedia.py#L523
this `beam.transforms.Reshuffle()` cause the memory error.

it makes sense if I consider the shuffle means. Beam's reshuffle seems need put all data in memory.
Previously I doubt that this line causes error, but at that time another bug showed in #2037 made error, so I can't found it.

Anyway, I comment out this line, and run load_dataset, then it works!

```python
wiki = datasets.load_dataset(
    "./wikipedia.py",
    cache_dir="./datasets",
    beam_runner="DirectRunner",
    language="ja",
    date="20210120",
)["train"]
```
![image](https://user-images.githubusercontent.com/6331508/112283369-6a9f3300-8ccb-11eb-82e5-827bf7fddfb9.png)

Dataset has already shuffle function. https://github.com/huggingface/datasets/blob/349ac4398a3bcae6356f14c5754483383a60e8a4/src/datasets/arrow_dataset.py#L2069
So, though I don't know it's difference correctly, but I think Beam's reshuffle isn't be needed. How do you think?