🤗 Transformers

要运行 🤗 Transformers 示例，请确保您已安装以下库

pip install datasets transformers torch evaluate nltk rouge_score

Trainer

evaluate 中的指标可以轻松地与 Trainer 集成。 Trainer 接受一个 compute_metrics 关键字参数，该参数传递一个函数来计算指标。可以在 TrainerArguments 中使用 evaluation_strategy 指定评估间隔，并且基于此，模型将相应地进行评估，并将预测和标签传递给 compute_metrics。

from datasets import load_dataset
from transformers import AutoTokenizer, AutoModelForSequenceClassification, TrainingArguments, Trainer
import numpy as np
import evaluate

# Prepare and tokenize dataset
dataset = load_dataset("yelp_review_full")
tokenizer = AutoTokenizer.from_pretrained("bert-base-cased")

def tokenize_function(examples):
    return tokenizer(examples["text"], padding="max_length", truncation=True)

tokenized_datasets = dataset.map(tokenize_function, batched=True)

small_train_dataset = tokenized_datasets["train"].shuffle(seed=42).select(range(200))
small_eval_dataset = tokenized_datasets["test"].shuffle(seed=42).select(range(200))

# Setup evaluation 
metric = evaluate.load("accuracy")

def compute_metrics(eval_pred):
    logits, labels = eval_pred
    predictions = np.argmax(logits, axis=-1)
    return metric.compute(predictions=predictions, references=labels)

# Load pretrained model and evaluate model after each epoch
model = AutoModelForSequenceClassification.from_pretrained("bert-base-cased", num_labels=5)
training_args = TrainingArguments(output_dir="test_trainer", evaluation_strategy="epoch")

trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=small_train_dataset,
    eval_dataset=small_eval_dataset,
    compute_metrics=compute_metrics,
)

trainer.train()

Seq2SeqTrainer

我们可以将 Seq2SeqTrainer 用于序列到序列的任务，例如翻译或摘要。对于此类生成任务，通常评估 ROUGE 或 BLEU 等指标。但是，这些指标要求我们使用模型生成一些文本，而不是像例如分类那样的单次前向传递。Seq2SeqTrainer 允许在使用 predict_with_generate=True 进行设置时使用 generate 方法，这将为评估集中的每个样本生成文本。这意味着我们在 compute_metric 函数中评估生成的文本。我们只需要先解码预测和标签。

import nltk
from datasets import load_dataset
import evaluate
import numpy as np
from transformers import AutoTokenizer, DataCollatorForSeq2Seq
from transformers import AutoModelForSeq2SeqLM, Seq2SeqTrainingArguments, Seq2SeqTrainer

# Prepare and tokenize dataset
billsum = load_dataset("billsum", split="ca_test").shuffle(seed=42).select(range(200))
billsum = billsum.train_test_split(test_size=0.2)
tokenizer = AutoTokenizer.from_pretrained("t5-small")
prefix = "summarize: "

def preprocess_function(examples):
    inputs = [prefix + doc for doc in examples["text"]]
    model_inputs = tokenizer(inputs, max_length=1024, truncation=True)

    labels = tokenizer(text_target=examples["summary"], max_length=128, truncation=True)

    model_inputs["labels"] = labels["input_ids"]
    return model_inputs

tokenized_billsum = billsum.map(preprocess_function, batched=True)

# Setup evaluation
nltk.download("punkt", quiet=True)
metric = evaluate.load("rouge")

def compute_metrics(eval_preds):
    preds, labels = eval_preds

    # decode preds and labels
    labels = np.where(labels != -100, labels, tokenizer.pad_token_id)
    decoded_preds = tokenizer.batch_decode(preds, skip_special_tokens=True)
    decoded_labels = tokenizer.batch_decode(labels, skip_special_tokens=True)

    # rougeLSum expects newline after each sentence
    decoded_preds = ["\n".join(nltk.sent_tokenize(pred.strip())) for pred in decoded_preds]
    decoded_labels = ["\n".join(nltk.sent_tokenize(label.strip())) for label in decoded_labels]

    result = metric.compute(predictions=decoded_preds, references=decoded_labels, use_stemmer=True)
    return result

# Load pretrained model and evaluate model after each epoch
model = AutoModelForSeq2SeqLM.from_pretrained("t5-small")
data_collator = DataCollatorForSeq2Seq(tokenizer=tokenizer, model=model)

training_args = Seq2SeqTrainingArguments(
    output_dir="./results",
    evaluation_strategy="epoch",
    learning_rate=2e-5,
    per_device_train_batch_size=16,
    per_device_eval_batch_size=4,
    weight_decay=0.01,
    save_total_limit=3,
    num_train_epochs=2,
    fp16=True,
    predict_with_generate=True
)

trainer = Seq2SeqTrainer(
    model=model,
    args=training_args,
    train_dataset=tokenized_billsum["train"],
    eval_dataset=tokenized_billsum["test"],
    tokenizer=tokenizer,
    data_collator=data_collator,
    compute_metrics=compute_metrics
)

trainer.train()

您可以将任何 evaluate 指标与 Trainer 和 Seq2SeqTrainer 一起使用，只要它们与任务和预测兼容即可。如果您不想训练模型而只想评估现有模型，则可以在上述脚本中将 trainer.train() 替换为 trainer.evaluate()。