[chinese wwm] load_datasets behavior not as expected when using run_mlm_wwm.py script
## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->

- `transformers` version: 4.7.0
- Platform: Linux-5.4.0-91-generic-x86_64-with-glibc2.29
- Python version: 3.8.10
- PyTorch version (GPU?): 1.10.0+cu102 (True)
- Tensorflow version (GPU?): 2.4.0 (True)
- Using GPU in script?: yes
- Using distributed or parallel set-up in script?: no

### Who can help
@LysandreJik @sgugger
 
## Information

Model I am using (Bert, XLNet ...): bert-base-chinese

The problem arises when using:
* [https://github.com/huggingface/transformers/blob/master/examples/research_projects/mlm_wwm/run_mlm_wwm.py] the official example scripts: `rum_mlm_wwm.py`

The tasks I am working on is: pretraining whole word masking with my own dataset and ref.json file
I tried follow the run_mlm_wwm.py procedure to do whole word masking on pretraining task. my file is in .txt form, where one line represents one sample, with `9,264,784` chinese lines in total. the ref.json file is also contains 9,264,784 lines of whole word masking reference data for my chinese corpus. but when I try to adapt the run_mlm_wwm.py script, it shows that somehow after 
`datasets["train"] = load_dataset(...`
`len(datasets["train"])` returns `9,265,365`
then, after `tokenized_datasets = datasets.map(...`
`len(tokenized_datasets["train"])` returns `9,265,279`
I'm really confused and tried to trace code by myself but can't know what happened after a week trial.

I want to know what happened in the `load_dataset()` function and `datasets.map` here and how did I get more lines of data than I input. so I'm here to ask.
## To reproduce
Sorry that I can't provide my data here since it did not belong to me. but I'm sure I remove the blank lines.

## Expected behavior
I expect the code run as it should. but the AssertionError in line 167 keeps raise as the line of reference json and datasets['train'] differs.

Thanks for your patient reading!
This script is not an actively maintained example, so you should ping the original contributor for any question on it :-)<|||||>@julien-c <|||||>@hyusterr  Sorry for late, I met the same question.
The file load by `load_dataset ()` is kind of diff from norm way, so just run the check as follows:

```python
for line in data:
    assert len(line.splitlines()) == 1
```
It works for me, hope it could help.<|||||>thanks for your information! I will try it.<|||||>I found that it's "^]" making the load_dataset to split more lines than expected, e.g.

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Thanks for your imformation!<|||||>I also meet the same problem. Hoping you can fix the code sometime. @wlhgtc <|||||>simply `splitlines()` can handle the problem<|||||>> 
Thanks for your information.