hf/transformers/docs/source/en/tasks/multiple_choice.mdx

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# Multiple choice

[[open-in-colab]]

A multiple choice task is similar to question answering, except several candidate answers are provided along with a context and the model is trained to select the correct answer.

This guide will show you how to:

1. Finetune [BERT](https://huggingface.co/bert-base-uncased) on the `regular` configuration of the [SWAG](https://huggingface.co/datasets/swag) dataset to select the best answer given multiple options and some context.
2. Use your finetuned model for inference.

<Tip>
The task illustrated in this tutorial is supported by the following model architectures:

<!--This tip is automatically generated by `make fix-copies`, do not fill manually!-->

[ALBERT](../model_doc/albert), [BERT](../model_doc/bert), [BigBird](../model_doc/big_bird), [CamemBERT](../model_doc/camembert), [CANINE](../model_doc/canine), [ConvBERT](../model_doc/convbert), [Data2VecText](../model_doc/data2vec-text), [DeBERTa-v2](../model_doc/deberta-v2), [DistilBERT](../model_doc/distilbert), [ELECTRA](../model_doc/electra), [ERNIE](../model_doc/ernie), [ErnieM](../model_doc/ernie_m), [FlauBERT](../model_doc/flaubert), [FNet](../model_doc/fnet), [Funnel Transformer](../model_doc/funnel), [I-BERT](../model_doc/ibert), [Longformer](../model_doc/longformer), [LUKE](../model_doc/luke), [MEGA](../model_doc/mega), [Megatron-BERT](../model_doc/megatron-bert), [MobileBERT](../model_doc/mobilebert), [MPNet](../model_doc/mpnet), [Nezha](../model_doc/nezha), [Nyströmformer](../model_doc/nystromformer), [QDQBert](../model_doc/qdqbert), [RemBERT](../model_doc/rembert), [RoBERTa](../model_doc/roberta), [RoBERTa-PreLayerNorm](../model_doc/roberta-prelayernorm), [RoCBert](../model_doc/roc_bert), [RoFormer](../model_doc/roformer), [SqueezeBERT](../model_doc/squeezebert), [XLM](../model_doc/xlm), [XLM-RoBERTa](../model_doc/xlm-roberta), [XLM-RoBERTa-XL](../model_doc/xlm-roberta-xl), [XLNet](../model_doc/xlnet), [X-MOD](../model_doc/xmod), [YOSO](../model_doc/yoso)

<!--End of the generated tip-->

</Tip>

Before you begin, make sure you have all the necessary libraries installed:

```bash
pip install transformers datasets evaluate
```

We encourage you to login to your Hugging Face account so you can upload and share your model with the community. When prompted, enter your token to login:

```py
>>> from huggingface_hub import notebook_login

>>> notebook_login()
```

## Load SWAG dataset

Start by loading the `regular` configuration of the SWAG dataset from the 🤗 Datasets library:

```py
>>> from datasets import load_dataset

>>> swag = load_dataset("swag", "regular")
```

Then take a look at an example:

```py
>>> swag["train"][0]
{'ending0': 'passes by walking down the street playing their instruments.',
 'ending1': 'has heard approaching them.',
 'ending2': "arrives and they're outside dancing and asleep.",
 'ending3': 'turns the lead singer watches the performance.',
 'fold-ind': '3416',
 'gold-source': 'gold',
 'label': 0,
 'sent1': 'Members of the procession walk down the street holding small horn brass instruments.',
 'sent2': 'A drum line',
 'startphrase': 'Members of the procession walk down the street holding small horn brass instruments. A drum line',
 'video-id': 'anetv_jkn6uvmqwh4'}
```

While it looks like there are a lot of fields here, it is actually pretty straightforward:

- `sent1` and `sent2`: these fields show how a sentence starts, and if you put the two together, you get the `startphrase` field.
- `ending`: suggests a possible ending for how a sentence can end, but only one of them is correct.
- `label`: identifies the correct sentence ending.

## Preprocess

The next step is to load a BERT tokenizer to process the sentence starts and the four possible endings:

```py
>>> from transformers import AutoTokenizer

>>> tokenizer = AutoTokenizer.from_pretrained("bert-base-uncased")
```

The preprocessing function you want to create needs to:

1. Make four copies of the `sent1` field and combine each of them with `sent2` to recreate how a sentence starts.
2. Combine `sent2` with each of the four possible sentence endings.
3. Flatten these two lists so you can tokenize them, and then unflatten them afterward so each example has a corresponding `input_ids`, `attention_mask`, and `labels` field.

```py
>>> ending_names = ["ending0", "ending1", "ending2", "ending3"]


>>> def preprocess_function(examples):
...     first_sentences = [[context] * 4 for context in examples["sent1"]]
...     question_headers = examples["sent2"]
...     second_sentences = [
...         [f"{header} {examples[end][i]}" for end in ending_names] for i, header in enumerate(question_headers)
...     ]

...     first_sentences = sum(first_sentences, [])
...     second_sentences = sum(second_sentences, [])

...     tokenized_examples = tokenizer(first_sentences, second_sentences, truncation=True)
...     return {k: [v[i : i + 4] for i in range(0, len(v), 4)] for k, v in tokenized_examples.items()}
```

To apply the preprocessing function over the entire dataset, use 🤗 Datasets [`~datasets.Dataset.map`] method. You can speed up the `map` function by setting `batched=True` to process multiple elements of the dataset at once:

```py
tokenized_swag = swag.map(preprocess_function, batched=True)
```

🤗 Transformers doesn't have a data collator for multiple choice, so you'll need to adapt the [`DataCollatorWithPadding`] to create a batch of examples. It's more efficient to *dynamically pad* the sentences to the longest length in a batch during collation, instead of padding the whole dataset to the maximum length.

`DataCollatorForMultipleChoice` flattens all the model inputs, applies padding, and then unflattens the results:

<frameworkcontent>
<pt>
```py
>>> from dataclasses import dataclass
>>> from transformers.tokenization_utils_base import PreTrainedTokenizerBase, PaddingStrategy
>>> from typing import Optional, Union
>>> import torch


>>> @dataclass
... class DataCollatorForMultipleChoice:
...     """
...     Data collator that will dynamically pad the inputs for multiple choice received.
...     """

...     tokenizer: PreTrainedTokenizerBase
...     padding: Union[bool, str, PaddingStrategy] = True
...     max_length: Optional[int] = None
...     pad_to_multiple_of: Optional[int] = None

...     def __call__(self, features):
...         label_name = "label" if "label" in features[0].keys() else "labels"
...         labels = [feature.pop(label_name) for feature in features]
...         batch_size = len(features)
...         num_choices = len(features[0]["input_ids"])
...         flattened_features = [
...             [{k: v[i] for k, v in feature.items()} for i in range(num_choices)] for feature in features
...         ]
...         flattened_features = sum(flattened_features, [])

...         batch = self.tokenizer.pad(
...             flattened_features,
...             padding=self.padding,
...             max_length=self.max_length,
...             pad_to_multiple_of=self.pad_to_multiple_of,
...             return_tensors="pt",
...         )

...         batch = {k: v.view(batch_size, num_choices, -1) for k, v in batch.items()}
...         batch["labels"] = torch.tensor(labels, dtype=torch.int64)
...         return batch
```
</pt>
<tf>
```py
>>> from dataclasses import dataclass
>>> from transformers.tokenization_utils_base import PreTrainedTokenizerBase, PaddingStrategy
>>> from typing import Optional, Union
>>> import tensorflow as tf


>>> @dataclass
... class DataCollatorForMultipleChoice:
...     """
...     Data collator that will dynamically pad the inputs for multiple choice received.
...     """

...     tokenizer: PreTrainedTokenizerBase
...     padding: Union[bool, str, PaddingStrategy] = True
...     max_length: Optional[int] = None
...     pad_to_multiple_of: Optional[int] = None

...     def __call__(self, features):
...         label_name = "label" if "label" in features[0].keys() else "labels"
...         labels = [feature.pop(label_name) for feature in features]
...         batch_size = len(features)
...         num_choices = len(features[0]["input_ids"])
...         flattened_features = [
...             [{k: v[i] for k, v in feature.items()} for i in range(num_choices)] for feature in features
...         ]
...         flattened_features = sum(flattened_features, [])

...         batch = self.tokenizer.pad(
...             flattened_features,
...             padding=self.padding,
...             max_length=self.max_length,
...             pad_to_multiple_of=self.pad_to_multiple_of,
...             return_tensors="tf",
...         )

...         batch = {k: tf.reshape(v, (batch_size, num_choices, -1)) for k, v in batch.items()}
...         batch["labels"] = tf.convert_to_tensor(labels, dtype=tf.int64)
...         return batch
```
</tf>
</frameworkcontent>

## Evaluate

Including a metric during training is often helpful for evaluating your model's performance. You can quickly load a evaluation method with the 🤗 [Evaluate](https://huggingface.co/docs/evaluate/index) library. For this task, load the [accuracy](https://huggingface.co/spaces/evaluate-metric/accuracy) metric (see the 🤗 Evaluate [quick tour](https://huggingface.co/docs/evaluate/a_quick_tour) to learn more about how to load and compute a metric):

```py
>>> import evaluate

>>> accuracy = evaluate.load("accuracy")
```

Then create a function that passes your predictions and labels to [`~evaluate.EvaluationModule.compute`] to calculate the accuracy:

```py
>>> import numpy as np


>>> def compute_metrics(eval_pred):
...     predictions, labels = eval_pred
...     predictions = np.argmax(predictions, axis=1)
...     return accuracy.compute(predictions=predictions, references=labels)
```

Your `compute_metrics` function is ready to go now, and you'll return to it when you setup your training.

## Train

<frameworkcontent>
<pt>
<Tip>

If you aren't familiar with finetuning a model with the [`Trainer`], take a look at the basic tutorial [here](../training#train-with-pytorch-trainer)!

</Tip>

You're ready to start training your model now! Load BERT with [`AutoModelForMultipleChoice`]:

```py
>>> from transformers import AutoModelForMultipleChoice, TrainingArguments, Trainer

>>> model = AutoModelForMultipleChoice.from_pretrained("bert-base-uncased")
```

At this point, only three steps remain:

1. Define your training hyperparameters in [`TrainingArguments`]. The only required parameter is `output_dir` which specifies where to save your model. You'll push this model to the Hub by setting `push_to_hub=True` (you need to be signed in to Hugging Face to upload your model). At the end of each epoch, the [`Trainer`] will evaluate the accuracy and save the training checkpoint.
2. Pass the training arguments to [`Trainer`] along with the model, dataset, tokenizer, data collator, and `compute_metrics` function.
3. Call [`~Trainer.train`] to finetune your model.

```py
>>> training_args = TrainingArguments(
...     output_dir="my_awesome_swag_model",
...     evaluation_strategy="epoch",
...     save_strategy="epoch",
...     load_best_model_at_end=True,
...     learning_rate=5e-5,
...     per_device_train_batch_size=16,
...     per_device_eval_batch_size=16,
...     num_train_epochs=3,
...     weight_decay=0.01,
...     push_to_hub=True,
... )

>>> trainer = Trainer(
...     model=model,
...     args=training_args,
...     train_dataset=tokenized_swag["train"],
...     eval_dataset=tokenized_swag["validation"],
...     tokenizer=tokenizer,
...     data_collator=DataCollatorForMultipleChoice(tokenizer=tokenizer),
...     compute_metrics=compute_metrics,
... )

>>> trainer.train()
```

Once training is completed, share your model to the Hub with the [`~transformers.Trainer.push_to_hub`] method so everyone can use your model:

```py
>>> trainer.push_to_hub()
```
</pt>
<tf>
<Tip>

If you aren't familiar with finetuning a model with Keras, take a look at the basic tutorial [here](../training#train-a-tensorflow-model-with-keras)!

</Tip>
To finetune a model in TensorFlow, start by setting up an optimizer function, learning rate schedule, and some training hyperparameters:

```py
>>> from transformers import create_optimizer

>>> batch_size = 16
>>> num_train_epochs = 2
>>> total_train_steps = (len(tokenized_swag["train"]) // batch_size) * num_train_epochs
>>> optimizer, schedule = create_optimizer(init_lr=5e-5, num_warmup_steps=0, num_train_steps=total_train_steps)
```

Then you can load BERT with [`TFAutoModelForMultipleChoice`]:

```py
>>> from transformers import TFAutoModelForMultipleChoice

>>> model = TFAutoModelForMultipleChoice.from_pretrained("bert-base-uncased")
```

Convert your datasets to the `tf.data.Dataset` format with [`~transformers.TFPreTrainedModel.prepare_tf_dataset`]:

```py
>>> data_collator = DataCollatorForMultipleChoice(tokenizer=tokenizer)
>>> tf_train_set = model.prepare_tf_dataset(
...     tokenized_swag["train"],
...     shuffle=True,
...     batch_size=batch_size,
...     collate_fn=data_collator,
... )

>>> tf_validation_set = model.prepare_tf_dataset(
...     tokenized_swag["validation"],
...     shuffle=False,
...     batch_size=batch_size,
...     collate_fn=data_collator,
... )
```

Configure the model for training with [`compile`](https://keras.io/api/models/model_training_apis/#compile-method):

```py
>>> model.compile(optimizer=optimizer)
```

The last two things to setup before you start training is to compute the accuracy from the predictions, and provide a way to push your model to the Hub. Both are done by using [Keras callbacks](../main_classes/keras_callbacks).

Pass your `compute_metrics` function to [`~transformers.KerasMetricCallback`]:

```py
>>> from transformers.keras_callbacks import KerasMetricCallback

>>> metric_callback = KerasMetricCallback(metric_fn=compute_metrics, eval_dataset=tf_validation_set)
```

Specify where to push your model and tokenizer in the [`~transformers.PushToHubCallback`]:

```py
>>> from transformers.keras_callbacks import PushToHubCallback

>>> push_to_hub_callback = PushToHubCallback(
...     output_dir="my_awesome_model",
...     tokenizer=tokenizer,
... )
```

Then bundle your callbacks together:

```py
>>> callbacks = [metric_callback, push_to_hub_callback]
```

Finally, you're ready to start training your model! Call [`fit`](https://keras.io/api/models/model_training_apis/#fit-method) with your training and validation datasets, the number of epochs, and your callbacks to finetune the model:

```py
>>> model.fit(x=tf_train_set, validation_data=tf_validation_set, epochs=2, callbacks=callbacks)
```

Once training is completed, your model is automatically uploaded to the Hub so everyone can use it!
</tf>
</frameworkcontent>


<Tip>

For a more in-depth example of how to finetune a model for multiple choice, take a look at the corresponding
[PyTorch notebook](https://colab.research.google.com/github/huggingface/notebooks/blob/main/examples/multiple_choice.ipynb)
or [TensorFlow notebook](https://colab.research.google.com/github/huggingface/notebooks/blob/main/examples/multiple_choice-tf.ipynb).

</Tip>

## Inference

Great, now that you've finetuned a model, you can use it for inference!

Come up with some text and two candidate answers:

```py
>>> prompt = "France has a bread law, Le Décret Pain, with strict rules on what is allowed in a traditional baguette."
>>> candidate1 = "The law does not apply to croissants and brioche."
>>> candidate2 = "The law applies to baguettes."
```

<frameworkcontent>
<pt>
Tokenize each prompt and candidate answer pair and return PyTorch tensors. You should also create some `labels`:

```py
>>> from transformers import AutoTokenizer

>>> tokenizer = AutoTokenizer.from_pretrained("my_awesome_swag_model")
>>> inputs = tokenizer([[prompt, candidate1], [prompt, candidate2]], return_tensors="pt", padding=True)
>>> labels = torch.tensor(0).unsqueeze(0)
```

Pass your inputs and labels to the model and return the `logits`:

```py
>>> from transformers import AutoModelForMultipleChoice

>>> model = AutoModelForMultipleChoice.from_pretrained("my_awesome_swag_model")
>>> outputs = model(**{k: v.unsqueeze(0) for k, v in inputs.items()}, labels=labels)
>>> logits = outputs.logits
```

Get the class with the highest probability:

```py
>>> predicted_class = logits.argmax().item()
>>> predicted_class
'0'
```
</pt>
<tf>
Tokenize each prompt and candidate answer pair and return TensorFlow tensors:

```py
>>> from transformers import AutoTokenizer

>>> tokenizer = AutoTokenizer.from_pretrained("my_awesome_swag_model")
>>> inputs = tokenizer([[prompt, candidate1], [prompt, candidate2]], return_tensors="tf", padding=True)
```

Pass your inputs to the model and return the `logits`:

```py
>>> from transformers import TFAutoModelForMultipleChoice

>>> model = TFAutoModelForMultipleChoice.from_pretrained("my_awesome_swag_model")
>>> inputs = {k: tf.expand_dims(v, 0) for k, v in inputs.items()}
>>> outputs = model(inputs)
>>> logits = outputs.logits
```

Get the class with the highest probability:

```py
>>> predicted_class = int(tf.math.argmax(logits, axis=-1)[0])
>>> predicted_class
'0'
```
</tf>
</frameworkcontent>