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# Text classification examples

This folder contains some scripts showing examples of *text classification* with the 🤗 Transformers library.
For straightforward use-cases you may be able to use these scripts without modification, although we have also
included comments in the code to indicate areas that you may need to adapt to your own projects.

## run_text_classification.py

This script handles perhaps the single most common use-case for this entire library: Training an NLP classifier
on your own training data. This can be whatever you want - you could classify text as abusive/hateful or 
allowable, or forum posts as spam or not-spam, or classify the genre of a headline as politics, sports or any 
number of other categories. Any task that involves classifying natural language into two or more different categories 
can work with this! You can even do regression, such as predicting the score on a 1-10 scale that a user gave,
given the text of their review.

The preferred input format is either a CSV or newline-delimited JSON file that contains a `sentence1` and 
`label` field, and optionally a `sentence2` field, if your task involves comparing two texts (for example, if your classifier
is deciding whether two sentences are paraphrases of each other, or were written by the same author). If
you do not have a `sentence1` field, the script will assume the non-label fields are the input text, which
may not always be what you want, especially if you have more than two fields! For example, here is a snippet
of a valid input JSON file, though note that your texts can be much longer than these, and are not constrained
(despite the field name) to being single grammatical sentences:
```
{"sentence1": "COVID-19 vaccine updates: How is the rollout proceeding?", "label": "news"}
{"sentence1": "Manchester United celebrates Europa League success", "label": "sports"}
```

### Usage notes
If your inputs are long (more than ~60-70 words), you may wish to increase the `--max_seq_length` argument
beyond the default value of 128. The maximum supported value for most models is 512 (about 200-300 words), 
and some can handle even longer. This will come at a cost in runtime and memory use, however.

We assume that your labels represent *categories*, even if they are integers, since text classification
is a much more common task than text regression. If your labels are floats, however, the script will assume
you want to do regression. This is something you can edit yourself if your use-case requires it!

After training, the model will be saved to `--output_dir`. Once your model is trained, you can get predictions
by calling the script without a `--train_file` or `--validation_file`; simply pass it the output_dir containing
the trained model and a `--test_file` and it will write its predictions to a text file for you.

### Multi-GPU and TPU usage

By default, the script uses a `MirroredStrategy` and will use multiple GPUs effectively if they are available. TPUs
can also be used by passing the name of the TPU resource with the `--tpu` argument.

### Memory usage and data loading

One thing to note is that all data is loaded into memory in this script. Most text classification datasets are small
enough that this is not an issue, but if you have a very large dataset you will need to modify the script to handle
data streaming. This is particularly challenging for TPUs, given the stricter requirements and the sheer volume of data
required to keep them fed. A full explanation of all the possible pitfalls is a bit beyond this example script and 
README, but for more information you can see the 'Input Datasets' section of 
[this document](https://www.tensorflow.org/guide/tpu).

### Example command
```
python run_text_classification.py \
--model_name_or_path distilbert-base-cased \
--train_file training_data.json \
--validation_file validation_data.json \
--output_dir output/ \
--test_file data_to_predict.json
```
