设置 `remove_unused_columns=False` 会导致 HuggingFace Trainer 类出错

问题描述

我正在使用 HuggingFace Trainer 类训练模型。以下代码做得不错：

!pip install datasets
!pip install transformers

from datasets import load_dataset
from transformers import AutoModelForSequenceClassification,TrainingArguments,Trainer,AutoTokenizer

dataset = load_dataset('glue','mnli')
model = AutoModelForSequenceClassification.from_pretrained('bert-base-uncased',num_labels=3)
tokenizer = AutoTokenizer.from_pretrained('bert-base-uncased',use_fast=True)

def preprocess_function(examples):
  return tokenizer(examples["premise"],examples["hypothesis"],truncation=True,padding=True)
encoded_dataset = dataset.map(preprocess_function,batched=True)

args = TrainingArguments(
    "test-glue",learning_rate=3e-5,per_device_train_batch_size=8,num_train_epochs=3,remove_unused_columns=True
  )

trainer = Trainer(
    model,args,train_dataset=encoded_dataset["train"],tokenizer=tokenizer
)
trainer.train()

但是，设置 remove_unused_columns=False 会导致以下错误：

ValueError                                Traceback (most recent call last)
/usr/local/lib/python3.7/dist-packages/transformers/tokenization_utils_base.py in convert_to_tensors(self,tensor_type,prepend_batch_axis)
    704                 if not is_tensor(value):
--> 705                     tensor = as_tensor(value)
    706 

ValueError: too many dimensions 'str'

During handling of the above exception,another exception occurred:

ValueError                                Traceback (most recent call last)
8 frames
/usr/local/lib/python3.7/dist-packages/transformers/tokenization_utils_base.py in convert_to_tensors(self,prepend_batch_axis)
    720                     )
    721                 raise ValueError(
--> 722                     "Unable to create tensor,you should probably activate truncation and/or padding "
    723                     "with 'padding=True' 'truncation=True' to have batched tensors with the same length."
    724                 )

ValueError: Unable to create tensor,you should probably activate truncation and/or padding with 'padding=True' 'truncation=True' to have batched tensors with the same length.

非常感谢任何建议。

解决方法

失败是因为value行中的705是一个str列表，指向hypothesis。而 hypothesis 是 ignored_columns 中的 trainer.py 之一。

/usr/local/lib/python3.7/dist-packages/transformers/tokenization_utils_base.py in convert_to_tensors(self,tensor_type,prepend_batch_axis)
    704                 if not is_tensor(value):
--> 705                     tensor = as_tensor(value)

有关 trainer.py 标志，请参阅来自 remove_unused_columns 的以下片段：

def _remove_unused_columns(self,dataset: "datasets.Dataset",description: Optional[str] = None):
    if not self.args.remove_unused_columns:
        return dataset
    if self._signature_columns is None:
        # Inspect model forward signature to keep only the arguments it accepts.
        signature = inspect.signature(self.model.forward)
        self._signature_columns = list(signature.parameters.keys())
        # Labels may be named label or label_ids,the default data collator handles that.
        self._signature_columns += ["label","label_ids"]
    columns = [k for k in self._signature_columns if k in dataset.column_names]
    ignored_columns = list(set(dataset.column_names) - set(self._signature_columns))

在标志为 False 的情况下，HuggingFace 上可能存在一个潜在的拉取请求以提供后备选项。但总的来说，标志实现似乎不完整，例如它不能与 Tensorflow 一起使用。

相反，保留它True并没有什么坏处，除非有特殊需要。