The metric takes a list of text as input, as well as the name of the model used to compute the metric:
from evaluate import load
perplexity = load("perplexity", module_type="metric")
results = perplexity.compute(predictions=predictions, model_id='gpt2')- model_id (str): model used for calculating Perplexity. NOTE: Perplexity can only be calculated for causal language models.
- This includes models such as gpt2, causal variations of bert, causal versions of t5, and more (the full list can be found in the AutoModelForCausalLM documentation here: https://huggingface.co/docs/transformers/master/en/model_doc/auto#transformers.AutoModelForCausalLM )
- predictions (list of str): input text, where each separate text snippet is one list entry.
- batch_size (int): the batch size to run texts through the model. Defaults to 16.
- add_start_token (bool): whether to add the start token to the texts, so the perplexity can include the probability of the first word. Defaults to True.
- device (str): device to run on, defaults to
cudawhen available
This metric outputs a dictionary with the perplexity scores for the text input in the list, and the average perplexity. If one of the input texts is longer than the max input length of the model, then it is truncated to the max length for the perplexity computation.
{'perplexities': [8.182524681091309, 33.42122268676758, 27.012239456176758], 'mean_perplexity': 22.871995608011883}
The range of this metric is [0, inf). A lower score is better.
perplexity = evaluate.load("perplexity", module_type="metric")
input_texts = ["lorem ipsum", "Happy Birthday!", "Bienvenue"]
results = perplexity.compute(model_id='gpt2',
add_start_token=False,
predictions=input_texts)
print(list(results.keys()))
print(round(results["mean_perplexity"], 2))
print(round(results["perplexities"][0], 2))perplexity = evaluate.load("perplexity", module_type="metric")
input_texts = datasets.load_dataset("wikitext",
"wikitext-2-raw-v1",
split="test")["text"][:50]
input_texts = [s for s in input_texts if s!='']
results = perplexity.compute(model_id='gpt2',
predictions=input_texts)
print(list(results.keys()))
print(round(results["mean_perplexity"], 2))
print(round(results["perplexities"][0], 2))Note that the output value is based heavily on what text the model was trained on. This means that perplexity scores are not comparable between models or datasets. See Meister and Cotterell, "Language Model Evaluation Beyond Perplexity" (2021) for more information about alternative model evaluation strategies.
@article{jelinek1977perplexity,
title={Perplexity—a measure of the difficulty of speech recognition tasks},
author={Jelinek, Fred and Mercer, Robert L and Bahl, Lalit R and Baker, James K},
journal={The Journal of the Acoustical Society of America},
volume={62},
number={S1},
pages={S63--S63},
year={1977},
publisher={Acoustical Society of America}
}