diff --git a/README.md b/README.md new file mode 100644 index 0000000..bb29a53 --- /dev/null +++ b/README.md @@ -0,0 +1,81 @@ +--- +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('joeddav/xlm-roberta-large-xnli') +tokenizer = AutoTokenizer.from_pretrained('joeddav/xlm-roberta-large-xnli') + +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] +```