使用TorchText库进行文本分类

比眉伴天荒 2023-01-16 14:24 451阅读 0赞

# 使用Torchtext库进行文本分类（官方的例子） #

配置：

torch                  1.8.1+cpu  
torchtext              0.9.1

官方文档的链接：[https://pytorch.org/tutorials/beginner/text\_sentiment\_ngrams\_tutorial.html][https_pytorch.org_tutorials_beginner_text_sentiment_ngrams_tutorial.html]

文章中关于AG\_NEWS数据集一会儿能加载出来，一会儿加载不出来（什么时候是否需要splite），我也没搞懂，感觉不是重点，有大佬懂的话可以在评论区讲一下哈（感谢）！

## （1）读入新闻类型的数据，这里使用的AG\_NEWS数据集 ##

由于直接使用官网下载会报错，先下载数据集，再使用下面的方法加载数据集

下载数据集的链接：**https://pan.baidu.com/s/1Rz\_XoaTZWSRiHGOwkACosQ  提取码：j0no **

数据集简介：4类新闻，分别是 World、 Sports、Business、Sci/Tec（依次用0-3表示）

csv文件有三列，分别是label、title、new

import torch
    from torchtext.datasets import AG_NEWS
    
    path = 'C:/Users/USER/Desktop/AG_NEWS.data'#改成你数据集存放的路径
    train_data, test_dataset = AG_NEWS(root=path, split=('train', 'test'))

## （2）构建词汇表 ##

from torchtext.data.utils import get_tokenizer
    from collections import Counter
    from torchtext.vocab import Vocab
    
    tokenizer = get_tokenizer('basic_english')
    train_iter = AG_NEWS(split='train')
    counter = Counter()
    for (label, line) in train_iter:
        counter.update(tokenizer(line))#统计每次词出现的频率
    vocab = Vocab(counter, min_freq=1)#构建词汇表，min_freq表示指定最小的频次是1
    #print(vocab.freqs) #查看词汇及其对应的频率
    
    #词汇表将token转换为整数
    for token in ['here', 'is', 'an', 'example']:#测试用例    
        print(vocab[token])

### **Vocab  待补充** ###

[https://pytorch.org/text/stable/vocab.html][https_pytorch.org_text_stable_vocab.html]

## （3）生成数据批处理和迭代器 ##

text\_pipeline、label\_pipeline建立文本、标签处理管道，用于处理来自数据集迭代器的原始数据字符串（转换为数值型）

text_pipeline = lambda x: [vocab[token] for token in tokenizer(x)]
    label_pipeline = lambda x: int(x) - 1
    #print(text_pipeline('here is the an example'))#文本管道，将字符串转换为索引，
    #输出：[475, 21, 2, 30, 5286]
    #print(label_pipeline('10'))#标签管道，将label转换为整数，输出：9
    
    def collate_batch(batch):
        label_list, text_list, offsets = [], [], [0]
        for (_label, _text) in batch:
             label_list.append(label_pipeline(_label))
             processed_text = torch.tensor(text_pipeline(_text), dtype=torch.int64)
             text_list.append(processed_text)
             offsets.append(processed_text.size(0))
        label_list = torch.tensor(label_list, dtype=torch.int64)
        offsets = torch.tensor(offsets[:-1]).cumsum(dim=0)
        text_list = torch.cat(text_list)
        return label_list.to(device), text_list.to(device), offsets.to(device)

collate\_fn函数将对从生成的一批样本起作用`DataLoader，`输入到的collate\_fn是一批数据，批处理大小为`DataLoader`，

并且collate\_fn根据先前声明的数据处理管道对原始数据进行处理。

注意：确保将collate\_fn其声明为顶级def。这样可以确保该功能在每个工作程序中均可用。

在本示例中，原始数据批处理输入中的文本条目被打包到一个列表中，

并作为输入的单个张量级联nn.EmbeddingBag

offset是定界符的张量，表示文本张量中各个序列的起始索引；

Label是一个张量，用于保存单个文本条目的标签；

**先得到三个列表：**

label\_list：batch中每个文本的标签， 如\[0，1, 2, 3\]

text\_list：batch的每个文本转换成词汇表的索引，如\[12,34,578, ...\]

offsets：batch中每个文本的长度，如\[10, 20, 30, 40\]

### 对 offsets = torch.tensor(offsets\[:-1\]).cumsum(dim=0)的测试 ###

直观理解，去掉最后一个，然后累加起来

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjI0MTQzOA_size_16_color_FFFFFF_t_70][]

### cat()的测试 ###

函数目的： 在给定维度上对输入的张量序列seq 进行连接操作

t1=\[1,2,3\]

t2=\[4,5,6\]

转换为tensor，然后进行拼接

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjI0MTQzOA_size_16_color_FFFFFF_t_70 1][]

## （4）定义神经网络模型 ##

该模型由nn.EmbeddingBag层和一个用于分类目的的线性层组成。

nn.EmbeddingBag默认模式为“均值”时，将计算结果嵌入“句袋”的平均值

此处的文本条目长度不同，nn.EmbeddingBag也能进行处理，因为文本长度以偏移量保存了下来。

下图表示模型结构，经过Word look-up table得到的词汇对应的索引，然后经过embeddingBag层、线性层，得到输出结果。

![../\_images/text\_sentiment\_ngrams\_model.png][.._images_text_sentiment_ngrams_model.png]

from torch import nn
    
    class TextClassificationModel(nn.Module):
    
        def __init__(self, vocab_size, embed_dim, num_class):
            super(TextClassificationModel, self).__init__()
            self.embedding = nn.EmbeddingBag(vocab_size, embed_dim, sparse=True)
            self.fc = nn.Linear(embed_dim, num_class)
            self.init_weights()
    
        def init_weights(self):
            initrange = 0.5
            self.embedding.weight.data.uniform_(-initrange, initrange)
            self.fc.weight.data.uniform_(-initrange, initrange)
            self.fc.bias.data.zero_()
    
        def forward(self, text, offsets):
            embedded = self.embedding(text, offsets)
            return self.fc(embedded)

### EmbeddingBag 待补充 ###

## （5）训练、评估和测试代码 ##

import time
    
    def train(dataloader):
        model.train()
        total_acc, total_count = 0, 0
        log_interval = 500
        start_time = time.time()
    
        for idx, (label, text, offsets) in enumerate(dataloader):
            optimizer.zero_grad()
            predited_label = model(text, offsets)
            loss = criterion(predited_label, label)
            loss.backward()
            torch.nn.utils.clip_grad_norm_(model.parameters(), 0.1)
            optimizer.step()
            total_acc += (predited_label.argmax(1) == label).sum().item()
            total_count += label.size(0)
            if idx % log_interval == 0 and idx > 0:
                elapsed = time.time() - start_time
                print('| epoch {:3d} | {:5d}/{:5d} batches '
                      '| accuracy {:8.3f}'.format(epoch, idx, len(dataloader),
                                                  total_acc/total_count))
                total_acc, total_count = 0, 0
                start_time = time.time()
    
    def evaluate(dataloader):
        model.eval()
        total_acc, total_count = 0, 0
    
        with torch.no_grad():
            for idx, (label, text, offsets) in enumerate(dataloader):
                predited_label = model(text, offsets)
                loss = criterion(predited_label, label)
                total_acc += (predited_label.argmax(1) == label).sum().item()
                total_count += label.size(0)
        return total_acc/total_count

### torch.nn.utils.clip\_grad\_norm\_(model.parameters(), 0.1) ###

这个函数的作用，将p范数进行归一化操作，归一到0.1，默认为2范数，从而使得parameters的参数的2范数和为0.1

## （6）main函数 ##

if __name__ == '__main__':
    
        train_iter = AG_NEWS(split='train')
        num_class = len(set([label for (label, text) in train_iter]))
        vocab_size = len(vocab)
        emsize = 64
        model = TextClassificationModel(vocab_size, emsize, num_class).to(device)#95812,64,4
    
    
        EPOCHS = 10
        LR = 5
        BATCH_SIZE = 64
    
        criterion = torch.nn.CrossEntropyLoss()
        optimizer = torch.optim.SGD(model.parameters(), lr=LR)
        scheduler = torch.optim.lr_scheduler.StepLR(optimizer, 1.0, gamma=0.1)
        total_accu = None
        train_iter, test_iter = AG_NEWS()
        train_dataset = list(train_iter)
        test_dataset = list(test_iter)
        num_train = int(len(train_dataset) * 0.95)
        split_train_, split_valid_ = \
            random_split(train_dataset, [num_train, len(train_dataset) - num_train])
    
        train_dataloader = DataLoader(split_train_, batch_size=BATCH_SIZE,
                                      shuffle=True, collate_fn=collate_batch)
        valid_dataloader = DataLoader(split_valid_, batch_size=BATCH_SIZE,
                                      shuffle=True, collate_fn=collate_batch)
        test_dataloader = DataLoader(test_dataset, batch_size=BATCH_SIZE,
                                     shuffle=True, collate_fn=collate_batch)
    
    #训练模块    
    for epoch in range(1, EPOCHS + 1):
            epoch_start_time = time.time()
            train(train_dataloader)
            accu_val = evaluate(valid_dataloader)
            if total_accu is not None and total_accu > accu_val:
                scheduler.step()
            else:
                total_accu = accu_val
            print('| end of epoch {:3d} | time: {:5.2f}s | '
                  'valid accuracy {:8.3f} '.format(epoch,
                                                   time.time() - epoch_start_time,
                                                   accu_val))
        #测试数据集评估模型
        print('Checking the results of test dataset.')
        accu_test = evaluate(test_dataloader)
        print('test accuracy {:8.3f}'.format(accu_test))
    
        #预测模块
        ag_news_label = {1: "World",
                         2: "Sports",
                         3: "Business",
                         4: "Sci/Tec"}
    
        ex_text_str = "MEMPHIS, Tenn. – Four days ago, Jon Rahm was \
            enduring the season’s worst weather conditions on Sunday at The \
            Open on his way to a closing 75 at Royal Portrush, which \
            considering the wind and the rain was a respectable showing. \
            Thursday’s first round at the WGC-FedEx St. Jude Invitational \
            was another story. With temperatures in the mid-80s and hardly any \
            wind, the Spaniard was 13 strokes better in a flawless round. \
            Thanks to his best putting performance on the PGA Tour, Rahm \
            finished with an 8-under 62 for a three-stroke lead, which \
            was even more impressive considering he’d never played the \
            front nine at TPC Southwind."
        model = model.to("cpu")
        print("This is a %s news" %ag_news_label[predict(ex_text_str, text_pipeline)])

###  scheduler = torch.optim.lr\_scheduler.StepLR(optimizer, step\_size=1.0, gamma=0.1) 调整学习率 ###

step\_size表示调整间隔，一般指的是epoch

lr = gamma\*lr

这里就是 5 0.5 0.05 0.005这样子进行调整

[https_pytorch.org_tutorials_beginner_text_sentiment_ngrams_tutorial.html]: https://pytorch.org/tutorials/beginner/text_sentiment_ngrams_tutorial.html
[https_pytorch.org_text_stable_vocab.html]: https://pytorch.org/text/stable/vocab.html
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjI0MTQzOA_size_16_color_FFFFFF_t_70]: /images/20221022/ac2d0e1186eb4a259865613cde35c0c3.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjI0MTQzOA_size_16_color_FFFFFF_t_70 1]: /images/20221022/751d9ce1d3c441abacd339e89a535846.png
[.._images_text_sentiment_ngrams_model.png]: /images/20221022/2717197a0213429db36b853b80845410.png