readme: ---
  license: mit
  thumbnail: https://huggingface.co/front/thumbnails/facebook.png
  pipeline_tag: zero-shot-classification
  datasets:
  - multi_nli
  ---
  
  # bart-large-mnli
  
  This is the checkpoint for [bart-large](https://huggingface.co/facebook/bart-large) after being trained on the [MultiNLI (MNLI)](https://huggingface.co/datasets/multi_nli) dataset.
  
  Additional information about this model:
  - The [bart-large](https://huggingface.co/facebook/bart-large) model page
  - [BART: Denoising Sequence-to-Sequence Pre-training for Natural Language Generation, Translation, and Comprehension
  ](https://arxiv.org/abs/1910.13461)
  - [BART fairseq implementation](https://github.com/pytorch/fairseq/tree/master/fairseq/models/bart)
  
  ## NLI-based Zero Shot Text Classification
  
  [Yin et al.](https://arxiv.org/abs/1909.00161) proposed a method for using pre-trained NLI models as a ready-made zero-shot sequence classifiers. The method works by posing the sequence to be classified as the NLI premise and to construct a hypothesis from each candidate label. For example, if we want to evaluate whether a sequence belongs to the class "politics", we could construct a hypothesis of `This text is about politics.`. The probabilities for entailment and contradiction are then converted to label probabilities.
  
  This method is surprisingly effective in many cases, particularly when used with larger pre-trained models like BART and Roberta. See [this blog post](https://joeddav.github.io/blog/2020/05/29/ZSL.html) for a more expansive introduction to this and other zero shot methods, and see the code snippets below for examples of using this model for zero-shot classification both with Hugging Face's built-in pipeline and with native Transformers/PyTorch code.
  
  #### With the zero-shot classification pipeline
  
  The model can be loaded with the `zero-shot-classification` pipeline like so:
  
  ```python
  from transformers import pipeline
  classifier = pipeline("zero-shot-classification",
                        model="facebook/bart-large-mnli")
  ```
  
  You can then use this pipeline to classify sequences into any of the class names you specify.
  
  ```python
  sequence_to_classify = "one day I will see the world"
  candidate_labels = ['travel', 'cooking', 'dancing']
  classifier(sequence_to_classify, candidate_labels)
  #{'labels': ['travel', 'dancing', 'cooking'],
  # 'scores': [0.9938651323318481, 0.0032737774308770895, 0.002861034357920289],
  # 'sequence': 'one day I will see the world'}
  ```
  
  If more than one candidate label can be correct, pass `multi_class=True` to calculate each class independently:
  
  ```python
  candidate_labels = ['travel', 'cooking', 'dancing', 'exploration']
  classifier(sequence_to_classify, candidate_labels, multi_class=True)
  #{'labels': ['travel', 'exploration', 'dancing', 'cooking'],
  # 'scores': [0.9945111274719238,
  #  0.9383890628814697,
  #  0.0057061901316046715,
  #  0.0018193122232332826],
  # 'sequence': 'one day I will see the world'}
  ```
  
  
  #### With manual PyTorch
  
  ```python
  # pose sequence as a NLI premise and label as a hypothesis
  from transformers import AutoModelForSequenceClassification, AutoTokenizer
  nli_model = AutoModelForSequenceClassification.from_pretrained('facebook/bart-large-mnli')
  tokenizer = AutoTokenizer.from_pretrained('facebook/bart-large-mnli')
  
  premise = sequence
  hypothesis = f'This example is {label}.'
  
  # run through model pre-trained on MNLI
  x = tokenizer.encode(premise, hypothesis, return_tensors='pt',
                       truncation_strategy='only_first')
  logits = nli_model(x.to(device))[0]
  
  # we throw away "neutral" (dim 1) and take the probability of
  # "entailment" (2) as the probability of the label being true 
  entail_contradiction_logits = logits[:,[0,2]]
  probs = entail_contradiction_logits.softmax(dim=1)
  prob_label_is_true = probs[:,1]
  ```
  