Transformers 文档

因果语言建模

Hugging Face's logo
加入 Hugging Face 社区

并获得增强的文档体验

开始使用

因果语言建模

语言建模有两种类型:因果型和掩码型。本指南将介绍因果语言建模。因果语言模型经常用于文本生成。您可以使用这些模型进行创意应用,例如选择您自己的文字冒险游戏,或者像 Copilot 或 CodeParrot 这样的智能编码助手。

因果语言建模预测词元序列中的下一个词元,模型只能关注左侧的词元。这意味着模型无法看到未来的词元。GPT-2 是因果语言模型的一个例子。

本指南将向您展示如何:

  1. DistilGPT2r/askscience 子集上的 ELI5 数据集上进行微调。
  2. 使用您的微调模型进行推理。

要查看支持此任务的所有架构和检查点,我们建议您查看 任务页面

在开始之前,请确保您已安装所有必要的库

pip install transformers datasets evaluate

我们鼓励您登录到 Hugging Face 帐户,以便您可以将模型上传并与社区共享。当出现提示时,输入您的令牌进行登录。

>>> from huggingface_hub import notebook_login

>>> notebook_login()

加载 ELI5 数据集

首先,使用 🤗 Datasets 库加载 ELI5-Category 数据集的前 5000 个示例。这样您就有机会进行实验并确保一切正常,然后再花费更多时间在整个数据集上进行训练。

>>> from datasets import load_dataset

>>> eli5 = load_dataset("dany0407/eli5_category", split="train[:5000]")

使用 train_test_split 方法将数据集的 train 分割为训练集和测试集。

>>> eli5 = eli5.train_test_split(test_size=0.2)

然后查看一个示例

>>> eli5["train"][0]
{'q_id': '7h191n',
 'title': 'What does the tax bill that was passed today mean? How will it affect Americans in each tax bracket?',
 'selftext': '',
 'category': 'Economics',
 'subreddit': 'explainlikeimfive',
 'answers': {'a_id': ['dqnds8l', 'dqnd1jl', 'dqng3i1', 'dqnku5x'],
  'text': ["The tax bill is 500 pages long and there were a lot of changes still going on right to the end. It's not just an adjustment to the income tax brackets, it's a whole bunch of changes. As such there is no good answer to your question. The big take aways are: - Big reduction in corporate income tax rate will make large companies very happy. - Pass through rate change will make certain styles of business (law firms, hedge funds) extremely happy - Income tax changes are moderate, and are set to expire (though it's the kind of thing that might just always get re-applied without being made permanent) - People in high tax states (California, New York) lose out, and many of them will end up with their taxes raised.",
   'None yet. It has to be reconciled with a vastly different house bill and then passed again.',
   'Also: does this apply to 2017 taxes? Or does it start with 2018 taxes?',
   'This article explains both the House and senate bills, including the proposed changes to your income taxes based on your income level. URL_0'],
  'score': [21, 19, 5, 3],
  'text_urls': [[],
   [],
   [],
   ['https://www.investopedia.com/news/trumps-tax-reform-what-can-be-done/']]},
 'title_urls': ['url'],
 'selftext_urls': ['url']}

虽然这看起来很多,但您实际上只对 `text` 字段感兴趣。语言建模任务很酷的一点是您不需要标签(也称为无监督任务),因为下一个词 *就是* 标签。

预处理

下一步是加载 DistilGPT2 分词器来处理 `text` 子字段。

>>> from transformers import AutoTokenizer

>>> tokenizer = AutoTokenizer.from_pretrained("distilbert/distilgpt2")

您会从上面的示例中注意到,`text` 字段实际上嵌套在 `answers` 中。这意味着您需要使用 `flatten` 方法从其嵌套结构中提取 `text` 子字段。

>>> eli5 = eli5.flatten()
>>> eli5["train"][0]
{'q_id': '7h191n',
 'title': 'What does the tax bill that was passed today mean? How will it affect Americans in each tax bracket?',
 'selftext': '',
 'category': 'Economics',
 'subreddit': 'explainlikeimfive',
 'answers.a_id': ['dqnds8l', 'dqnd1jl', 'dqng3i1', 'dqnku5x'],
 'answers.text': ["The tax bill is 500 pages long and there were a lot of changes still going on right to the end. It's not just an adjustment to the income tax brackets, it's a whole bunch of changes. As such there is no good answer to your question. The big take aways are: - Big reduction in corporate income tax rate will make large companies very happy. - Pass through rate change will make certain styles of business (law firms, hedge funds) extremely happy - Income tax changes are moderate, and are set to expire (though it's the kind of thing that might just always get re-applied without being made permanent) - People in high tax states (California, New York) lose out, and many of them will end up with their taxes raised.",
  'None yet. It has to be reconciled with a vastly different house bill and then passed again.',
  'Also: does this apply to 2017 taxes? Or does it start with 2018 taxes?',
  'This article explains both the House and senate bills, including the proposed changes to your income taxes based on your income level. URL_0'],
 'answers.score': [21, 19, 5, 3],
 'answers.text_urls': [[],
  [],
  [],
  ['https://www.investopedia.com/news/trumps-tax-reform-what-can-be-done/']],
 'title_urls': ['url'],
 'selftext_urls': ['url']}

每个子字段现在都是一个单独的列,如 `answers` 前缀所示,而 `text` 字段现在是一个列表。与其单独分词每个句子,不如将列表转换为字符串,以便您可以一起分词它们。

这是一个用于连接字符串列表并分词结果的第一个预处理函数。

>>> def preprocess_function(examples):
...     return tokenizer([" ".join(x) for x in examples["answers.text"]])

要将此预处理函数应用于整个数据集,请使用 🤗 Datasets 的 map 方法。您可以设置 `batched=True` 来一次处理多个数据集元素,并通过 `num_proc` 增加进程数量来加速 `map` 函数。删除任何您不需要的列。

>>> tokenized_eli5 = eli5.map(
...     preprocess_function,
...     batched=True,
...     num_proc=4,
...     remove_columns=eli5["train"].column_names,
... )

此数据集包含词元序列,但其中一些长度超过了模型允许的最大输入长度。

您现在可以使用第二个预处理函数来

  • 连接所有序列
  • 将连接的序列分割成由 `block_size` 定义的较短的块,`block_size` 应该比最大输入长度短,并且足够短以适应您的 GPU 内存。
>>> block_size = 128


>>> def group_texts(examples):
...     # Concatenate all texts.
...     concatenated_examples = {k: sum(examples[k], []) for k in examples.keys()}
...     total_length = len(concatenated_examples[list(examples.keys())[0]])
...     # We drop the small remainder, we could add padding if the model supported it instead of this drop, you can
...     # customize this part to your needs.
...     if total_length >= block_size:
...         total_length = (total_length // block_size) * block_size
...     # Split by chunks of block_size.
...     result = {
...         k: [t[i : i + block_size] for i in range(0, total_length, block_size)]
...         for k, t in concatenated_examples.items()
...     }
...     result["labels"] = result["input_ids"].copy()
...     return result

将 `group_texts` 函数应用于整个数据集。

>>> lm_dataset = tokenized_eli5.map(group_texts, batched=True, num_proc=4)

现在使用 DataCollatorForLanguageModeling 创建一个示例批次。在批次处理过程中动态填充句子到批次中最长的长度比将整个数据集填充到最大长度更有效。

使用序列结束词元作为填充词元,并将 `mlm` 设置为 `False`。这将使用输入作为标签,并向右移动一个元素。

>>> from transformers import DataCollatorForLanguageModeling

>>> tokenizer.pad_token = tokenizer.eos_token
>>> data_collator = DataCollatorForLanguageModeling(tokenizer=tokenizer, mlm=False)

训练

如果您不熟悉使用 Trainer 微调模型,请查看 基本教程

您现在可以开始训练您的模型了!使用 AutoModelForCausalLM 加载 DistilGPT2。

>>> from transformers import AutoModelForCausalLM, TrainingArguments, Trainer

>>> model = AutoModelForCausalLM.from_pretrained("distilbert/distilgpt2")

此时,只剩下三个步骤

  1. TrainingArguments 中定义您的训练超参数。唯一必需的参数是 output_dir,它指定了保存模型的位置。您将通过设置 push_to_hub=True 将模型推送到 Hub(您需要登录 Hugging Face 才能上传模型)。
  2. 将训练参数与模型、数据集和数据收集器一起传递给 Trainer
  3. 调用 train() 来微调您的模型。
>>> training_args = TrainingArguments(
...     output_dir="my_awesome_eli5_clm-model",
...     eval_strategy="epoch",
...     learning_rate=2e-5,
...     weight_decay=0.01,
...     push_to_hub=True,
... )

>>> trainer = Trainer(
...     model=model,
...     args=training_args,
...     train_dataset=lm_dataset["train"],
...     eval_dataset=lm_dataset["test"],
...     data_collator=data_collator,
...     processing_class=tokenizer,
... )

>>> trainer.train()

训练完成后,使用 evaluate() 方法来评估您的模型并获取其困惑度。

>>> import math

>>> eval_results = trainer.evaluate()
>>> print(f"Perplexity: {math.exp(eval_results['eval_loss']):.2f}")
Perplexity: 49.61

然后使用 push_to_hub() 方法将您的模型分享到 Hub,以便每个人都可以使用您的模型。

>>> trainer.push_to_hub()

有关如何微调因果语言模型以进行训练的更深入示例,请查看相应的 PyTorch 笔记本

推理

太棒了,现在您已经微调了模型,您可以将其用于推理了!

构思一个您想生成文本的提示。

>>> prompt = "Somatic hypermutation allows the immune system to"

尝试对微调后的模型进行推理的最简单方法是将其用于 pipeline()。使用您的模型实例化一个用于文本生成的 `pipeline`,然后将您的文本传递给它。

>>> from transformers import pipeline

>>> generator = pipeline("text-generation", model="username/my_awesome_eli5_clm-model")
>>> generator(prompt)
[{'generated_text': "Somatic hypermutation allows the immune system to be able to effectively reverse the damage caused by an infection.\n\n\nThe damage caused by an infection is caused by the immune system's ability to perform its own self-correcting tasks."}]

对文本进行标记并返回 input_ids 作为 PyTorch 张量

>>> from transformers import AutoTokenizer

>>> tokenizer = AutoTokenizer.from_pretrained("username/my_awesome_eli5_clm-model")
>>> inputs = tokenizer(prompt, return_tensors="pt").input_ids

使用 generate() 方法生成文本。有关不同文本生成策略和控制生成的参数的更多详细信息,请查看 文本生成策略页面。

>>> from transformers import AutoModelForCausalLM

>>> model = AutoModelForCausalLM.from_pretrained("username/my_awesome_eli5_clm-model")
>>> outputs = model.generate(inputs, max_new_tokens=100, do_sample=True, top_k=50, top_p=0.95)

将生成的 token ID 解码回文本

>>> tokenizer.batch_decode(outputs, skip_special_tokens=True)
["Somatic hypermutation allows the immune system to react to drugs with the ability to adapt to a different environmental situation. In other words, a system of 'hypermutation' can help the immune system to adapt to a different environmental situation or in some cases even a single life. In contrast, researchers at the University of Massachusetts-Boston have found that 'hypermutation' is much stronger in mice than in humans but can be found in humans, and that it's not completely unknown to the immune system. A study on how the immune system"]
在 GitHub 上更新

© . This site is unofficial and not affiliated with Hugging Face, Inc.